When trying to analyze an animal's body language, each signal must be taken in context. Other body language signals should be analyzed as well to form as complete as possible view of the animal's intent or emotional state. You can generally characterize signs in 3 categories: go, stop and yield. 

The paw lift is one of those body language signals that must be interpreted based on context. The best interpretation of this body language signal is anticipation or uncertainty about the situation. The dogs is anticipating something and the dogʼs go button is pressed. She could be anticipating a treat from her owner or she could be ready to spring forward and bite her owner. By interpreting the rest of her body language, you can figure out which way she will go.

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The dog with his paw lifted is anticipating play. This is an easy one because he is also exhibiting a play bow.

This dog has his ears slightly back indicating that he is slightly worried or anxious. He is anticipating the approach of the veterinarian looking at him. This anticipation is met with fear and anxiety.

The yellow dog is anticipating a treat from the person sitting in front of her. She has her mouth open and he head lifted because she is barking at the person for attention. She is not a threat.

The puppy in this photo has her paw raised as she greets an older, more confident dog. The confident dog is not threatening her, but is alert. The puppy is leaning away and averting her gaze to show that she is not a threat, but her body is relaxed and her tail is up showing that she is not extremely fearful.She is lifting her paw either in anticipation that the older dog will play with her or possibly to show discomfort with the body language of the older dog. This interaction ended with play. Courtesy: Carol A. Siegrist, CDBC, CBCC-KA, CPDT-KA http://www.dogtraininginthecity.com/