How to determine whether "and" or "or" is correct when listing excluded entities?

This is not so simple as it first seems. The use of or is unambiguous: trucks or buses are excluded, whether singly or together.

The use of and is not so clear-cut. Its interpretation depends on context and detail. Consider:

No cars and trailers.

No mothers and buggies.

The use of the conventionally acceptable and meaningful noun phrases cars and trailers or mothers and buggies excludes neither cars nor trailers, neither mothers nor buggies.

In the case of trucks and buses, the noun phrase trucks and buses is not in conventional use so the sign has to be taken to exclude them singly.