It's totally okay to discuss other websites - we even have a whole subforum dedicated to that:
Community Sites Discussion - Menewsha
As far as helping friends find you elsewhere, that's ok too. If you are leaving your active Mene RPs for another site, I'm sure your peeps would appreciate you letting them know so of course that's okay. :) Linking to your profile on another site is okay in signatures and such; but for referral links the general rule is that you can share them with someone who specifically asks (we prefer you send the referral link via PM) - at this time, we don't want referral links in signatures because that's something that everyone sees every time you post.
The main thing to know is that we don't want people sending
unsolicited recruiting messages (like spamming folks who didn't request them with links). Or, like, advertising threads from other sites here. Or only being here to try to get other folks to leave.
Does that help? If there's a specific/more detailed thing you're wanting to do that feels like it's in a grey area and you'd like to run it by me, go ahead and send me a PM. :)