Like tear stains or what? You really didn't give much information so I don't think anyone is really going to be able to tell you what's going on.
Look up tear stains and see if you think that's what your dog has. Those are pretty common.
If it's not that, or is bad or seems painful, take your dog into the vet and get their opinion. Eyes are a very sensitive organ and if your dog has an infection or some kind of eye problem it could really bother him.