I remember reading a thread or article some time ago where thieves would find out where and when shooting competitions were taking place. They would walk the parking lots at the club or range where the competition was taking place. Since members at the clubs didn't know the visiting shooters, they weren't suspicious of extra people in the lots. The thieves would place a small mark or sticker on cars in the parking lots where the owner wouldn't necessarily notice them.
If the competition was local, they would follow the cars or cruise neighborhoods to spot the cars. They then knew which homes had guns and would break in later to steal them. If it was a regional or national competition, they would cruise the hotel lots to spot the cars and break in, figuring the guns would be in the trunk as the owners might be uncomfortable carrying them through the hotel lobby, even in cases. They also knew that if it was a regional or national competition, the guns would be high end and expensive.
The moral of the story is...be aware when attending any gun related events.
As for advertising with any stickers, whether NRA or manufacturer, DON'T. You're letting scumbags know you have guns. You open yourself up to the scenario above while at home or traveling.
In addition, my area, we are close to the border crossings with Canada, which is very liberal and anti-gun. There are nice beaches, summer cottages, and a fairly short ride to Toronto, offering Broadway quality theaters, Major League Baseball, etc. I know of people who shoot and proudly displayed NRA stickers on their vehicles. Notice I stated "displayed" in the past tense. They were questioned vigorously at the Customs/Immigration booth about their guns and whether they had them in the vehicle. Then they were pulled over for secondary inspections EVERY TIME they crossed the border. They weren't stupid enough to have their guns, magazines or even an extra bullet in the car or truck, so no harm, no foul....but they just got tired of being detained EVERY TIME.
Not long after, they took the gun related stickers off of their cars, and guess what.....never even got asked or pulled over since, not in years!
Again, never advertise.... and remember this acronym... CANT... "Carry Always Never Tell".