I see your point. But you've got to admit, that a can of ANY paint would be fairly easy to come by. And if Marcus' goal is to "turtle up" then this little detail overlooked will surely lead to his demise. I mean some distance greater than 2 miles away is a sign pointing to their location ...

Of course what would make the turtle theory work (for me) is if the Colony did not block the roads ... what if either the Zombies or other humans were trying to prevent humans from getting there (or getting out)? If you've ever played Left 4 Dead and had a tank throw a car at you, then you have to ask yourself why couldn't a big nasty one nudge a car into the road? Heck, a smart one drove a tanker. What if that was part of a larger plan by "INK" to isolate the colony? Or prevent their rescue (maybe to Sea?). Or if the scouts are trying to prevent more from coming into the camp. That would mean the Colony has truly been holed up and was not right next to the sign placing roadblocks but leaving rescue signs up.

Also, my point about the guarding is that the threat of being fed to the Zombies should negate the need to have armed guards over the work crews. Instead we have a situation sooo bad that we can assume at least some of the people would gladly choose to temp fate on their own then stay there. Now, we get to see how bad that is ....