Any chance this could be a failed\disturbed bike theft, rather than a disgruntled tenant? I know it seems unlikely given that the bike wasn't moved far, but if I thought there was a chance that it may have been a tenant (and I can't possibly read anything negative into tenement either btw
) then perhaps a small piece of paper into each mailbox stating what has happened for the tenants suggesting that they ring the police if they see anything untowards going on with bikes on their railings. May make them rethink their strategy too, if it was one of them...