Hasty House Hunting on the Horizon?

My roommates and I were very surprised to come home last night to this sign in our front lawn.

Not even a word of warning from the landlord to any of us residents. Inconsiderate and just plain not cool.

We'll check the (now month-to-month) lease for a (hopefully) mandatory advance notice by the landlord prior to making us vacate, but I guess we might be in the market for new living arrangements soon...

Any suggestions?