Indeed there has been a change. After the forum software upgrade, it was possible for users to post in colors, and thus (with intention or not) were able to post in blue or green, which was misleading for users to determine if a post was official or not.
Also described in the Forum guide here:
http://forum.us.runesofmagic.com/showthread.php?t=68917
Blue/Green/Font Color
Color allocation forms part or our forum organization activities, allowing you to recognize posts from moderators, mentors and community managers by color. CM, QA and other Runes of Magic team members write in blue (although sometimes in red) and mentors write in green. Normal players, i.e. your fellow players write in black. Altering font color and style is deactivated for all regular users which means that it is easier to see official posts from us.
So the user rights on forums were changed. Apparently, this effects signatures as well. I am not sure if it is possible by the software to separate between post and signature, but I will ask. For now, Signatures are affected by the same rule-set.