I don't know exactly what I look for. The bully breeds I just know, but even little pups...if they just look at you with no body or tail wiggle I am going to ask first. But if you walk up to any pup any size and the wag starts at the tail and works it's way up...ditto if dogkins hits the ground or cart belly up. THAT is a friendly dog.

The only time I may stroke a dog without asking is at the dog park where all the dogs are loose and you really don't even know what dog belongs to who when one walks up to you. I will never pet a leashed or restrained dog without asking. And admittedly, I will never pet some types of dogs regardless. Chihuahuas for example. The dog may be totally friendly, but I shan't be petting a Chihuahua.

People have done it to my Nigredo countless times. They may pass by and say HI to him, and he will look at them and wag his curly fluffy tail and they just immediately go to work on him. He's an extremely friendly dog who invites everyone to stroke him or tap his side and say GOOD BOY! Several have knelt down etc. as well. One lady just bent all the way down and hugged him 'round the neck and then vigorously rubbed his sides, all the while saying random high pitched gibberish to him. He was SO happy!

I never say anything such as "You really should ask first", I just look on with a smile and answer any questions they ask me about him. It's not a big deal to me because he loves the attention. I don't take my snarky dog around lots of people, and if I have to, such as if she sees the vet or something, she is muzzled and people know to leave her alone.