Colorado states the law doesn't uphold signs at a local business for no concealed carry. In other words it's not a violation of state law to carry into a business that's posted. Only if they somehow discover you're carrying, ask you to leave and you refuse are you breaking the law.
"“No Firearm” signs in Colorado have no force of law unless they are posted on property that is specifically mentioned in State Law as being off limits to those with a Permit/License to Carry. If you are in a place not specifically mentioned in the law that is posted and they ask you to leave, you must leave. If you refuse to leave then you are breaking the law and can be charged. Even if the property is not posted and you are asked to leave you must leave. Always be aware of the possibility that responding Police Officers who may have been called without your knowledge and may not know the laws on trespass etc. could arrest you even if you are within the law.
Carry In State Parks/State & National Forests/WMA"
http://handgunlaw.us/states/colorado.pdf