Are there preserved inscriptions or other such texts from ancient Rome that contain a prohibition? I would prefer original signs that have survived, but mentions in the literature are also interesting. I am looking for something like "don't walk on the grass" or "do not enter"; it should be a prohibition, not an order ("return dishes here") nor a warning ("beware of the dog").
I don’t think there is any attestation of a direct prohibition of the no smoking type for the classical period. The closest I could find is CIL VI, 2357, from Rome, but it is not a prohibition, it is a kind request:
HOSPES AD HUNC TUMULUM NI MEIAS OSSA PRECANTUR TECTA HOMINIS SET SI GRATUS HOMO ES MISCE BIBE DA MI
NI=ne, SET=sed, MI=mihi
Passerby, the buried bones of a man ask you not to piss on this tomb, but if you are a well-mannered man, pour, drink, and give me (wine).
The interesting fact is that the very same text from HOSPES to PRECANTUR is repeated in CIL IV, 8899, from Pompeii, followed by obscene jokes: it might be a direct reference to this specific inscription, but it might also be some kind of well known set phrase. In this case, we would have an idiomatic way to express a specific prohibition.
A famous Greek example: Plato supposedly put a sign over the door to his school reading
ἀγεωμέτρητος μηδεὶς εἰσίτω,
“May no one ignorant of geometry enter here”
“Geometriae ignarus nullus ingrediatur”.
The story is apparently apocryphal (see: https://www.persee.fr/doc/reg_0035-2039_1968_num_81_384_1013).