Okay. Now that we've established that I'm a fan of symbols and ornaments as visible/tangible reminders of the things we need to be doing, let's talk about the other piece of this.
People of color are pointing out that the safety pin thing looks an awful lot like armchair activism meant to make white people feel better without actually doing anything. And I totally agree. If all you're doing is pinning a bit of metal onto yourself so you can tell yourself that you're doing SOMETHING, you are not being an activist and you are not being an ally, and you need to stop that right now and go find something actually useful to do.
(There's going to be links to resources at the end of the post, and I invite everyone but especially my fellow white cis people to help me find more of those.)
You don't get to call yourself an ally; you have to earn it by BEING an ally and constantly working to be a better one, which includes listening when someone tells you you've messed up and then taking steps to do better in the future. You also don't get to call yourself an activist unless you're actually doing the work.
There is a learning curve on this stuff. There are also a lot of different ways to do the work, and everybody has to figure out what they can do. Many of us are marginalized in some ways while being privileged in others; I'm a disabled queer Jewish woman, yes, but I'm also a white middle-class cisgender American citizen with no accent and mostly invisible disabilities, and if I take off my Star of David and don't talk about religion it's not obvious that I'm Jewish.
If you're a person with privilege wearing a safety pin as a symbol of your commitment to healing the world, I'm going to challenge you to the same thing I'm challenging myself to do in wearing it: step up your game and get out of your comfort zone. Do more. If you're already out there working to make things better, take on one more thing. If you've largely lived inside a bubble of privilege and this is the first time you're consciously making the choice to get involved in social justice, read through the posts I'm going to share in just a minute, make sure you understand what you're promising to do, and then pick at least two OTHER things to start doing in the meantime.
But don't stop there. Do as much good as you can, in as many ways as you can, every time that you can.
Here are some suggestions for immediate things to work on if you're wearing a safety pin: start practicing what you can say and do, so you don't freeze up in the moment. If you aren't familiar with the concepts of non-violent communication and conflict resolution, I encourage you to go read up on them. (If anybody has good resources for that, toss them into the comments, please.) I strongly believe in using peaceful de-escalation and diversion whenever you can.
Consider other ways you can be visible about your commitment to social justice. Friends have pointed out that this is a very easy symbol for hate groups to co-opt; what can you do to make it more obvious that you are wearing it in good faith? For me, so far that means wearing it alongside my #IllGoWithYou button and Jewish star and rainbow ribbons; I'm still thinking about what else I can do. Pin it onto a Black Lives Matter t-shirt or wear it next to a peace sign or hamsa. (Don't fall into cultural appropriation in the process, though, please, and for the love of all that is holy please don't try to reclaim the swastika. I know it was originally a symbol of peace, and I am normally ALL about reclamation as a form of power, but that one is too far gone.)
Don't back away from hard conversations, and don't ignore microaggressions. Call on your family and friends to join you in taking action. If you're a parent, talk to your child about how what they should do if you're called upon to help someone. Decide if there are times or places where you can't wear one, and remember that being able to stop being visible is a huge form of privilege.
Symbols have power. Symbols are important. But they don't do the work. You do.
Here's a very incomplete list of things that I think you should read if you're going to be wearing a safety pin as a symbol. I'll keep adding to it, and I invite you to share links in the comments.
Responding to Everyday Bigotry (very comprehensive document from the Southern Poverty Law Center)
This list of things white friends have done to make this person feel safer (Twitter thread; if the link doesn't work I can screenshot or storify or something)
Your Safety Pin Is Not Enough (article on Medium by a POC)
So You Want To Wear A Safety Pin (extremely practical suggestions written by a WOC)
What To Do If You See Islamophobic Harassment (wonderful comic by a French Middle Eastern woman; the tactics are useful for just about any sort of situation where someone is being harassed)
suggestions for a way white middle-aged women can use their privilege as a diversion (Facebook post by my friend Kate, a fellow disabled female artist)
11 Ways To Be A Trans* Ally (collection of 101-level tips from trans* people)
The Compassionate Listening Project (website of a non-profit organization working to build peace through understanding)
My laptop battery is about to die and my child just dumped water onto the trackpad which is making it act funny, and my headache is reaching the point where I'm about to lose coherent language entirely, so I'm going to stop for now. I know this is incomplete. I know you may disagree with some or all of what I've said, and I want you to know that I am listening. I'm going to go put on my own oxygen mask right now; I'll be back.
Thank you for joining me in thinking about difficult things. I hope you'll also join me in doing whatever we can to heal the world. It is not incumbent upon us to finish the work, but neither are we free to refrain from beginning it.
 When I get angry my Southern accent suddenly goes from juuuuuust barely there to very obvious and I start blessing people's hearts left and right, but that really does not count.
 And by "hate groups" I mean actual white supremacy groups like the KKK.