Regarding the general rules of the forum, it is not allowed to place ref links in posts - although there are exceptions in the form of someone opening an ANN thread which, if I'm not mistaken, can contain a ref link. Also, a few years ago there were some members who literally spammed the Gambling board with their ref links, but they were apparently allowed to do so - I think I even opened a thread on Meta about it.
It will immediately be reported to mods once someone post a ref link lbut wearing them under your signature is allowed if I'm not mistaken? Only if you do not participate in the eXch campaign, or does it also apply to non-participants?