"End of route" is a road sign (Diagram 965 in TSRGD) which traffic engineers use to mean "we've given up on this cycle path now, you're on your own from here."
As it is composed of white text on a blue rectangle, it is an advisory rather than compulsory. It's sometimes combined with the Cyclists Dismount sign which means "we really did have no idea what to do here, perhaps you should get off and push?"
Transport for London's new London Cycling Design Standards describes this sign, with others like 'Cyclists Dismount', as signs that
are confusing, unnecessary, or in some way compromise wider objectives of promoting safety, comfort, coherence and directness in cycling ...
‘End’ signing and ‘Cyclists Dismount’ signs should not be used because they show that consideration for cyclists has simply ended.