I think it’s risky if you live in the UK. We have a law called the Communications Act which has broad powers banning posting of anything which is ‘grossly offensive’. It’s entirely up to a court to decide what is ‘grossly offensive’ on a case-by-case basis.

In Scotland, it tends to indicate your political beliefs. People flying the Union Jack are normally unionists and supporters of the monarchy, whereas people flying the Saltire (Scottish) flag are normally nationalists (pro-independence). It’s therefore difficult to fly a flag ‘neutrally’ unless you were to fly both.