My physics is seriously rusty, but I would have thought that an SNR of single-digit dB is poor - checking, I have SNR of 280dB on one connection that's currently doing an epggrab, and 844 on the other that's conveniently just kicked in.
Lower is worse. SNR of 0 means that your noise is now the same as your signal... I think... so higher numbers are better if my logic holds.