Hint 3 - When dogs meet, a wealth of information passes between them through their scent glands between their toes behind their ears above and below their tails together with lots of body language. There is one key signal between them that I look for all the time.
Answer Hint 3 - I mentioned it in Hint 1, It is my equal sign". That is when the two bodies go parallel with each other looking in the same direction. It may only be witnessed for a second or two or it can be extended. Sometimes they go bounding together in this way, I'm sure you have seen that. Sometimes one is wanting to show it, and the other not, or not accepting, and the dog wanting to demonstrate will keep throwing their hip in while rotating clock or anti-clockwise. When this position is accepted between the dogs, they can play and rough and tumble and no harm will come to them. Good fun!