Just a thought, spurred on by some uploaded pictures by SilverRay

It would be useful when uploading pictures of lamps, particularly unusual or rare ones to include something that would give people an idea of the size.

One can use ruler or Size AA battery as for the scale of these bulbs.  They are wonderful to show how big these unusual bulbs are

Yep. Rulers, average 60 watt light bulbs, AA batteries, your arm or hands are all good comparison objects.

I've got a carpenter's Framing Square in my eBay watch list that we'll be able use to as a guide for the size of lamps. 

Tape measure as well

Tape measure as well

Yes, we do have one that we can use, but a framing square will let you show width and depth of a lamp at the same time. 

And for just under £3 you can't go wrong. 

I generally use a fluorescent starter.

@Mandolin Girl

Why don't you just go to the hardware store?

Because I wanted one with proper measurements... 
Feet and inches. 

I generally include the shape code (eg A-19, BT-56) in my lamp uploads which denotes the size and lamp shape for more common lamps. I suppose for less common stuff I have a 6 inch metal rule I could include in the frame.

For really big ones like large MH lamps and large fixtures you could use a standard 20w, 32w, or 40w fluorescent tube that probably everyone here has seen at some point or another.