In article , "Dorothy Bradbury"
says...
snip

If you have a vapour deposited brass letterbox without a knocker,
or no knocker or doorbell, couriers *love* to bang on glass panels.
Rattling a spring loaded flap doesn't do it for them, they want to use
it as a pager to you, the dead & the next life by acoustics alone.

When they break leaded glass again they'll be put in the next life G.

The Parcelforce bloke seemed really shocked when I told him what I'd do
if he knocked on my leaded light with his keys again - it seemed to get
the message across though. :-)