Ah yes ok I can understand that. I can see from a marketing point of view that you might want to simply and quietly avoid the (roughly) 1 in 1,000,000 ids which start with 4 specific characters.

Still, it's a bit culturally specific. It gives the impression of solving a problem that is doesn't. Depending on your market/language a different character might be a better choice. Plus there are quite a few 'bad' words that can still appear.

Filtering and rejecting proposed IDs based on a list of objectionable words seems like a far more realistic solution, then baking a very specific exclusion into the plumbing.