Welcome. First and foremost, know the laws in CO. CO is generally an OC friendly state, but it's kind of starting to get tougher. Denver city and county is a no-no. It's illegal, so don't bother.
Signs do not carry force of law, but you can be trespassed if you try to argue. If you OC in a place and are asked to leave, leave. Don't argue, don't complain. Post the location and send letters, etc.
As for the M&G's well, that's a semi-long story. A very large contingent of the CO group left OCDO a couple months ago over he constant bickering and a few out of state members here who claim to know everything there is to know about everything and hijacking threads etc, etc. LONG story. Anyway, there is a more CO centered location if you're interested. Some of the members frequent both places, some refuse to even read OCDO anymore. I'll send you a PM.