Once every 18 - 24 months the 200-inch mirror is pulled from the telescope to be re-aluminumized. When that happens the old coating of aluminum is removed and the mirror's honeycombed underside is revealed.
Apparently on July 20, 1936 someone wrote on the underside of the glass. Have a look at this unusual looking down through the glass to the underside:
The photo was reversed to make it easier to read the writing. I can't quite make out the first line. The second one reads:
July 20 - 1936
and the third says:
and I am not sure about the 4th. Any ideas?
Of course, this isn't the only example of graffiti on the 200-inch mirror.