Second, just below the lamps are signs pointing the way to London, Wimbledon, Wandsworth and Croydon.
The third feature is less obvious at a glance. Look more carefully at the base, though, and you will see that it is made up of four ventilation panels. These originally provided fresh air to toilets below, although those facilities are now gone.
I couldn't spot a foundry mark on the lamp (although my search did harvest a few odd looks from passers-by!). However, it is quite similar to a combined lamp and ventilation shaft on Strand, opposite the Royal Courts of Justice. In fact, the resemblance is great enough that it is probable they were made by the same firm, Walter Macfarlane of Glasgow. The addition of the signs, though, makes Peckham's example a little bit more special.
Tooting's lamp/signpost/ventilation cover is so special, in fact, that it is Grade II listed. Not bad for a piece of Victorian street furniture.