It's imprecise and there's overlap. However, to me (U.S. native speaker):
1) "To spot" suggests that you are actively looking and trying to find something specific.
2) "To notice" suggests that you're just passively watching, and suddenly became aware of something.
"What was the street number of that house we just passed?"
"I'm sorry, I didn't notice. I wasn't looking for street numbers."
"Well, see if you can spot one, so we can get some idea of how close we are to #605."
"Hey, I just noticed that we crossed Division Street. Does that help?"
"Yes, it does. Try to spot Washington Street, that's the last big street we'll be crossing, then start watching for house numbers."