As someone who has a dog that just won't shut up and has dealt with neighbors on it, here's my suggestion.
First, not all dogs are good inside when folks are away at work and school. My lab doesn't know how to be quiet outside, but cannot stay inside by himself. He EATS everything...toys, wall molding, speaker wire, etc. He has to be outside. He's grown out of a lot of that as he's gotten older, but not the barking.
The owner of the dog may not be aware of it...we weren't when it started because he didn't bark when we were home, because he was inside with us. We noticed he would bark when we got home, but whose dog doesn't when their owner arrives home?
My suggestion, write a note and sign your name. Give them your address so they can talk to you. Eventually, with neighborhood gossip you figure out who the anoynymous complainer is. The woman in our neighborhood who did the annoynmous letters also managed to write them on two of the worst days...the day I was in the hospital losing my babies and the day my husband lost his job. Dogs are sensitive and I know "Jack" knew there was something wrong the day I was in the hospital...I'm sure that's why even with his bark collar on, he was barking. If she had put her address down, we could have explained this to her...and by the way her note was so rude I didn't care she was annoyed. I'd kind of like to take a blow horn and blow it outside her house all night.
So...write a nice note, let the neighbor know and then tape it to their door with your name on it. If you can't man up to sign your name, then you shouldn't complain. Chances are they have no idea and will do what we did, tried a citronella collar, that didn't work, thied a shock collar, that did...and my husband tested it on himself too before giving to our dog.
So, there's my two cents...
-M