There used to be kerb crawler signs on Christchurch / Hillside corners.
Haven't seen much evidence of sex workers there for a long time, and no warning sign.
Maybe a dangerous assumption but I think they move to closer to the location of the latest crack-house. For instance for last couple of months there have been a few hanging around in the mornings at the Brixton Hill end of Upper Tulse Hill. In times past (many years) there were grouping around top of Brixton Hill/ New Park Road with a den allegedly being on Lyham Road.
It's all very sad