Perhaps you could stick an object at the entrance to the minefield and again at the entrance to the jumpgate, that looks enough out of place that people will check the infocard to see what it is. Then have on the infocard something that says:
"Restricted Area. Anyone not authorised by the Liberty Navy or Liberty Security Force will be destroyed, no questions asked.
OOC Note: Entering this zone means you can be destroyed on sight by any Liberty Navy or Liberty Security Force personnel (Must have [SA] or =LSF= in their name), regardless of your ID, tag or level."