Signese

Validating . . .

请勿让狗在此拉狗屎。

1) Dog owners.

2) Don't let your dog poop here.

This is a useful sign. I'm inspired to write it on the walls of my apartment complex.

I didn't understand the last word, but based on the the rest of the sentence I had good idea what message was trying to be conveyed. I guess someone here lost their patience and just had to write it. Hopefully they'll never visit Paris...

That last character is 屎 if you want to look it up. Could be a bit unclear given the medium and angle.

Do people in the real world use 勿 verbally in Mandarin? The word is replaced by 不要 in the Mandarin announcements in HK subway stations. For example, in Cantonese it is “請勿靠近車門" but in Mandarin it is “請不要靠近車門".

I suspect it's the same, you'd use 不要 in announcements. Beijing subway says 请不要依靠车门 if I remember correctly.

They should have one for humans too.

They do, you even commented on it.