I think these points are worth mentioning to the town council:
1) In the U.S., the federal government has officially established Christmas as a federal holiday.
2) Even from a non-religious position, one should recognize the fact that Jesus is a historical figure whose life and teachings have had an enormous and incalculable amount of influence throughout the world, including in the U.S. Even non-Christians and atheists would have to admit that.
3) The story of his birth is related in the number one best selling book in the U.S. (indeed, in the world) which, of course, is the Bible. It is also mentioned several times
in the Qur’an.
4) Muslims and many Jews consider Jesus a prophet and therefore, objectively speaking, have reason to commemorate his birth. In light of this, even though it arose as a Christian image, a creche does not represent only Christianity.
Therefore, the way that I see it, there should be no problem in having a creche on public land. It is simply a visible representation of a federally mandated holiday. IMO, it makes little sense to say that it is ok for the federal government to mandate a holiday in commemoration of the birth of Jesus, but then say it is
not ok to display a creche in commemoration of the birth of Jesus on public land. Whatever argument a person has against returning the creche to the Gettysburg town square would likewise be an argument against Christmas being a federal holiday in the first place, but few (if any) people want to take this issue that far.
Nevertheless, the members of your town council may be sympathetic to returning the creche to the town square but be unwilling to do so unless the legality of it is first firmly established. For example, the creche which was traditionally displayed in front of a government building in Canonsburg (also in your state) was moved to private property after someone made a complaint. The local officials simply wanted to avoid a potentially expensive court battle. You can read about this situation in
this link (and I invite you to compare Meagan Hartly’s anti-creche statements in that article with my pro-creche statements above).