Hmm toughie. I have the same job of trying not to sound like a complete insane animal loving mentalist most days in school when I'm questioned about my not so personal and highly controversial views on everything animal-wise.
On a public place like that it will be hard to get everyones attention/trust because everyone I have noticed needs to be tackled in a different way when it comes to something animal related.
This is a really general break down of the three main categories I put people in. There is more but these are the most common, apart from those who are impossible to talk to, I have come across in my preaching hours
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Person A - Genuinly interested/concerned
These people will take notice when you add in the "aww" factor. With these people and with the situation you are in I would definatly mention "puppies/kittens" the things people subcoinciously relate to with "cute" "sweet". Things like "dogs that just want a chance to prove themselves to people, and even proove to themselves that they can learn to love again".
Person B - Ignorent - ignores any issues because its too much to deal with
These people definatly do better with large stats. But you HAVE to be accurate, quote a source maybe to get trust. This is made up off the top of my head but something like "70% of the dogs in shelters that are put down are perfectly healthy" or "Fact: Each dog that is brought by a breeder, costs the life of one in the pound" (this also will get persons A attention). Go with a nice large stat that will grab their attention, but again, make sure it's a real stat.
Person C - Shallow/Materialistic
It might not sound like a charming label but it's the best way to describe Person C. They are more intested in a designer pet than a pet as a companion. These are the people that are most likely to not even think about rescues and head for breeders. I have a very close friend who is a Person C, it is highly frustrated but the way to get through to them is to turn the whole situation around and make it about them. How will THEY benefit from ignoring breeders and going to a rescue? Talk about advantages for them.
If you have a range of bits and bobs from all of those "People sections" you will definatly get more people trusting the article/advert you put up. You want the aww factor but not to a obvious degree, advantages for them personally and a few facts/stats (preferably sourced) that will grab the most stubborn of peoples attention.
Hope that helps.