No the signs are still there, there are 6 of them along T5, though 2 of them were moved slightly over to the side. Here is what they say:

https://www.flyertalk.com/forum/brit...-allowace.html

If you are departing LHR or LGW and you baggage is inside the HBO size limits then you can check your bags in for free in the usual way. But you can't use this to increase your 2 bag HBO limit and it applies to trips within Europe. It is not just for busy flights, from LHR or LGW.

In other scenarios such as departing from mainland Europe you normally need to get a text and SMS from BA allowing this. At the gate (past security) most places are OK for you to gate check bags unless the flight is half empty.