Not so much a support question rather a question about ROBLOX support for Unicode.
Refer the the default/user toggle at the bottom of the image - is using a Unicode checkmark (U+2713) inside of strings an acceptable practice? The checkmark is stored inside of a LUA variable, and changed via script, not via studio properties.
If the support is not there, use decals if possible.
It seems to work fine so far in studio on my PC - I’d like to eliminate as many images as possible 
, That’s the next option though, obviously.
I see, just keep your thumbs up, and hope for support. Otherwise you have to do it the hard way, with decals, obviously.
Roblox is installed along with the fonts it uses. The checkmark will work on all platforms.
