They serve as a signalling mechanism all right; they signal that their owner has no taste, and doesn't care.
Fashion is about signaling not whatever you happen to agree with.
Tattoos aren’t universal, what’s acceptable for Army special forces, goths, gang members, etc are all different. So, good or bad only exists in a specific context it isn’t something that any person can judge universally. Someone really can define good as whatever pisses people like you off.