Some years ago I was fascinated by a set of keys that somehow had ended their useful days on a bus shelter roof just outside what was the the local tax office.

I wondered for days how they got there; whose they were; what they did, it was, from what I could gather from the top deck of the bus, a collection of various sized keys. Utilitarian Yale lock keys, stern mortise keys, maybe a car key thrown on the loop, and possibly hidden out of sight, a set of suitcase keys.

I threw around notions of who the owner might have been; the one I finished on was that it was someone on a stag night, insensible with booze, with a ball and chain tied to his ankle, and whose mates had in that toe-curling Brit phrase thrown his house keys on to the bus shelter roof "for a laugh".

That was several years ago. The shelter's no longer there, so where the keys are now is any one's guess. Perhaps there's a place where all lost and forgotten keys gather.

It's rare that I get so enamoured of such marginalia, but I have seen something this week that's similarly piqued my curiosity: a rough heart drawn in a messy off-cut of concrete on Cornhill, one of the busiest streets in the City. It's heart that's maybe drawn with a finger in just setting concrete with the initials R and J around it.

Who are R and J? When was it done? Are they still together? How many millions of feet have pattered over this symbol of eternal love?