One page on that site concerns the price-codes of Bernard Quaritch Ltd. a business that is still going strong in London, despite several changes of premises since being founded by Bernard Quaritch himself in London in 1847.
Looking at images on Harvard University's Houghton Library website recently, I found a few images that all illustrate a particular type of Quaritch annotation, that can be useful in identifying manuscripts they sold in the early decades of the 20th century.
Once you've seen a few, they are easily recognisable, so it seemed worth putting them one after another here:
|Houghton MS Typ 201 [source]|
|Houghton MS Typ 131 [source]|
|Houghton MS Typ 180 [source]|
Here is one more from a non-Houghon MS:
EDIT, 16 December 2015:
Today Laura Cleaver directed me to a digitized manuscript that has an example of this sort of number, but superseded by a second number:
EDIT, 27 December 2015