If You See A YELLOW RIBBON on a Dog's Leash~Anyone with an infirmed, unsocial or elderly dog is going to love The Yellow Dog Project, a global movement for parents of dogs that need space. The concept behind it is simple. If you see a dog with a yellow ribbon it signifies a dog who needs space & you shouldn't attempt to pet or bring your own dog over for a greeting. It's an idea long overdue. http://www.care2.com/causes/what-to-do-if-you-see-a-yellow-ribbon-on-a-dogs-leash.html#ixzz2ZnAzfS3Z
Your dog might just be excited and being a little too friendly - but if he/she jumps up on people and cannot be controlled, it can be a nuisance or possibly even a problem. Some people might just not like having the dog jump up or may even be afraid.