I have been informed that posting links in chatter is only allowedby moderators, and for good reason. In case there are links to malicious websites shared here. but as far as i know we all have been doing this for a very long time. This is the first i have heard of it.
though the forum does not have a clear set of rules that i know of? i was informed by a moderator that chatter rules are applicable in the forum, though posting links is not explicitly stated in the chatter rules as unallowable. This rule is common knowledge, so to speak. But nowhere is the rules for the forum recorded.
though again the rules are never mentioned and are quite vague.
So my suggestion is official,general forum rules to clear up any confusion.