I made this a good few months back, and the response I got elsewhere was so powerful, I figured it should be useful to a fair few people!
this is intended for use on anything that may pose a risk of transformation occurring when interacting with it. the symbol is inspired by existing trefoil hazard symbols, as well as the alchemical symbol for projection (aka transmutation), which is pisces ♓︎.
the file here is 1200 wide, which should be enough for most purposes. in world I expect this to often be a fluorescent green, but any contrasting color should be readable. the exact color chosen here was so it'd print fine (CMY percents are in the filename).
if you want to use it yourself, consider it CC-BY-NC*. that is, you can use it in anything non-commercial, just make sure I get credit for the symbol in some way! meanwhile, if you use it for something you're selling, that's also fine with credit, as long as you're using it in a larger work; don't sell the symbol by itself, or as the major point of the thing being sold. (thus the little asterisk)
hope you enjoy!
edit to add: I keep getting asked about tattoos of this, so yes, if you want it on your body, go right ahead!
people have boosted this here and there lately, so I've been thinking about this symbol a lot more than usual. also thinking about making other symbols like it that'd appear in a setting of mine, might make one or two of those soon
