Anybody who know's London well will have seen some of its blue plaques.
They're a quiet memorial to some of the great and the good who have lived in the city through the years.
If you see one on a house in London and take a moment to read it, it'll tell you about famous people from the past who have lived there. There are roughly 900 of them scattered around various boroughs and they're adding new ones all the time. Freddie Mercury's plaque is being installed later this year in Feltham, West London.
Poets, play writers, authors, aviators to name a few. Their legacy's woven into the architectural fabric of London forever. The scheme has been running for 150 years this year. The charity that looks after them recently called for more female nominations as women are only featured on 12% of the plaques.
To be eligible for a nomination, the person has to have lived in a surviving building within greater London and been dead more than 20 years.
Next time you're in London, look out for the blue plaques!