Again, no they don't. You can only be charged with trespassing if asked to leave, and you don't. Ask any Cop or Lawyer, or better yet cite one instance of a person being charged for walking past a gun buster sign. The reason you must be asked to leave first is because the signs do NOT have force of law (hence, no gun charge), if they did none of that would be needed. I suggest you join the VCDL and go to some of the meetings when they have PD's and lawyers as guest speakers and brush up.
§ 18.2-308 Section O:
The granting of a concealed handgun permit shall not thereby authorize the possession of any handgun or other weapon on property or in places where such possession is otherwise prohibited by law or is prohibited by the owner of private property
Because signs have NO force of law in VA, Even in the case of semi-private (typically Businesses who do NOT own the property) a posted sign doesn't LEGALLY prohibit you from carrying, which is why if you don't leave when asked your charged with trespassing because that's the only LAW you broke. While I don't support business that are anti, there is a VERY big difference in carrying past a gun buster in a state with legal signs vs not. You would also notice that legal signs (in states that have them) are standardized and list the law or ordinance that they are enforcing.