This has nothing to do with the legend of the hay fever fellow the sign writer asked for a suggestion for a road name. The earliest ha-ha’s were walls with ditches so sheep found them harder to clamber over to reach the lettuce. They were fashionable among posh people who wanted to keep peasants out without obstructing their views across the countryside.
The original ha-ha’s were in Saint-Louis-du-Ha! Ha! In Quebec, so this may have something to do with reindeer saying “ha-ha, that’s never going to keep me out”. Has anybody tipped off this London borough about this? We wouldn’t want reindeer poo in Greenwich.