It's not a first amendment issue.
The first amendment just says that the government can't make a law to shut me up.
There is no law that says a landlord can't make rules that limit my speech.
Landlords have to take extreme care with "protected classes".
And forbidding BLM displays would push that envelope hard.
Too hard in the current political climate (I think).
My lawyer and I chatted about it for a while and he's got a buddy at the ACLU who would love to make my acquaintance.
But Alpine has not taken the bait.