If these are your neighbors, you will be well-served to build a civil, if not outright friendly relationship with them. Go over and make nice, explain the situation politely, you'll likely get a more positive response than just sticking a note on their door. That could be interpreted as disrespectful or cowardly.
My new neighbors parks in street and makes it almost impossible for me to get in my driveway without hitting their car, esp. when there is snow.. Should I go to their house and ask them nicely or write them a letter. I don't have their phone number?