There are two possible.explanations for this window sticker.
1. This mother is telling the truth in hopes that others will shame her son into being a better person, like when father Tom Jordan posted a video to Facebook that ended with him blowing his teenage daughter's laptop to pieces with a .45 handgun, or mother Jane Hambleton who sold her son's car after finding alcohol in it:
https://www.dispatch.com/story/news/2008/01/09/meanest-mom-sells-teenage/23305770007/
2. This mother's son is just fine, and she's just trying to scare away would-be troublemakers, like those shirts that say "To avoid injury-don't tell me how to do my job."