You can't advertise that you have controlled goods for sale, either by post, signature or PM. This includes direct advertising as well as inderect references. The same is true for sollicitating buying said parts.
This is applicable all over the board, in every non-AV'd section. We have a special AV-only section where sales are sometimes discussed outside of the formal WTS/WTB format, but since it's only us, it's tolerated.
Discussing a trade that is in progress or that is over doesn't advertise an available item, so there is no issue as long as it stays in the context of that specific exchange.