Trademarks can be used to describe the thing they name by people other than the trademark owner. That is, you don't have to say "that annual 26.2 mile race in the capital of Massachusetts" even though the Boston Athletic Association controls the "Boston Marathon" trademark. Photographs of things with logos on them can be analogous — you may take a photo of a Starbucks sign. You can't, however, try to mislead coffee customers with your photo.

Remember, trademark laws are consumer protection laws. They're there to prevent fraud. They are not intended as a way for people to monetize phrases or to take control of a portion of the public sphere.

Limiting photographs just because they happen to have logos would have a chilling effect on free speech and be directly contradictory to the First Amendment.

In your particular case, your photograph is a commentary on the product — as you describe it, the juxtaposition of the ambulance and the ice cream store reflects on the health of the ice cream sold — this is clearly a speech issue, and while I am not a lawyer it is my opinion as a citizen that you have a very strong free speech argument. There are McDonald's trademarks all over the film Super Size Me, and the company can't be very happy about it, but that's okay. If, on the other hand, you're trying to sell a photograph specifically by taking advantage of the familiarity of a company's trademark, that's probably not okay.

Stock photos are a special case, because a) the photos are likely to be used commercially, b) customers want generic so other logos don't confuse the message, and c) the agencies probably over-paranoid and not interested in getting in a lawsuit over your free speech rights.