http://offa.org/ will list OFA and CERF numbers.
A dog with an elbow number is normal. If there is elbow displaysia, no number is assigned. The number consists of a breed code (e.g., LR), the letters "EL" indicating this is an elbow test, a sequence number, the letter M or F to indicate the dog's gender, a two digit number indicating the dog's age in months, and an indicator of whether the dog is permanently identified (-PI).
For hips, the number has several elements. In the following number, LR-162859E25F-PI, the "PI" tells you the dog is permanently identified. The 25F tells you that the dog was 25 months old when xrayed and is female. The letter before that, "E", tells you the dog's hips are rated excellent. The first two letters "LR" tell you this is a labrador retriever. The middle part of the number is simply a sequence number. (The example is actually one of my dogs).
Edit:
Detailed information on CERF tests and numbers is at
http://www.vmdb.org/cerf.html. The number is simply a breed code (LR) followed by a sequence number. While the OFA site lists the CERF numbers, which are only assigned if the dog is clear of genetic defects, it does not list "breeder option" codes which are also worth looking at. These can be looked up directly on the CERF site which also provides explanations of the different codes.