if...
I would think that one who posts on any of these boards should be weary of it in the first place. I think if you are smart, you never get too specific of emails, names, locations...
If you have an email through the board, hopefully, you did not register with your real name and address. Paranoia is something good, not bad. It keeps your ass out of trouble. Everyone here could be narcs, looking for me, and with that mentality, nobody could ever get too close.
Law enforcement can not issue supeona's based on what one wrote on a message board. However, if they know where you are, and that you are up to something, you could get watched. And if you are careful never to say anything over the telephone or on emails or careful that everything is always consealed in a safe place that officers do not have right to search, then your ass will stay out of trouble.
A narc could be anywhere and are probably everywhere, so keep that in mind next time you talk on your cell phone.
Paranoid in some unknown land-
Dieslgrl