My two cents: The property owner certainly has the right to display the sign, and the right to feel the way he does about Obama (or Romney for that matter). Aside from that, the sign really doesn't affect anything, because how would the guy know if someone carrying a gun supported Obama or not, although I don't understand how anyone who respects the 2nd Amendment could vote for a candidate who is not pro-gun, Democrat or Republican.
I have to agree with WalkingWolf that I have no interest in getting along or compromising with the people who I see as political and ideological enemies. Trying to get along is why we're in the trouble we're in. We feel like we are lucky because we're beginning to get back gun rights we had before politicians and do-gooders decided guns were bad? Thats like gasoline going to $ 4.00 a gallon, then being thankful when it goes down to $3.00, when you know it should be $2.00!! The same folks who rail against our 2nd Amendment rights are the ones who preach tolerance for gay marriage, abortion on demand, support for illegals, etc. Its not enough that they don't want to own guns, they don't want me to own them either. Tolerance extends only to the rights they approve of and support, otherwise, its screw you. They don't just want control of their lives, they want to control your too.
The majority of Americans these days are sheep, willing to concede their beliefs and values (if they have any) in order to "get along". They're more concerned with making sure they have the latest Iphone or what the Kardashians are doing than with the state of our nation. If you disagree with my ideology, I have a few choices; I can try to sway you to see it as I do, I can leave you alone, or if you try to force your ideas on me or threaten my rights, I can fight you. What I'm saying is, if you are anti-gun, Republican or Democrat, black, white , or orange, yo're the enemy.