Hmm. In our area, these high school signs stay up all year round. It isn't unusual at all. They go up in August and don't come down until after graduation. In fact, many homes have several signs for band members, football players, choir members, etc. It's completely tradition and absolutely typical.

I would never buy a home in an HOA community for this kind of stupid petty crap.

That said, I would write a letter to the HOA voicing my frustration with the enforcement changing simply to appease the quarrel of two specific residents, and I would suggest that since it has previously been acceptable practice, the HOA might consider altering their rules about the timelines for such signs that might be a reasonable compromise, still support the schools and students, and create a time parameter for the future use of such signs. I'd probably still take it down in the meantime, but I'd very surely put it up again in the weeks surrounding graduation.

HOA's are petty, snoopy, controlling organizations. LOL.