DuchessofBrittany said:

I believe Marble Arch is situated somewhere close to where Tyburn used to be. I've never seen a plaque or any memorial, but could have missed it.

DOB, the original stone cross memorial (on the traffic island @ the junction of Edgware and Bayswater roads) was removed during road refurbishments in the summer of 2008. No replacement was put in place during the rest of that year and discussions were still taking place regarding plans for a new memorial during 2009. Pressure was put on City Hall to put this memorial on site as soon as possible but, if you visited this site during 2008/2009, it would explain why you never saw any memorial at that time.