The signature used comes from Max Newman’s visitor book, as displayed below:

Solution

The key is that each letter is followed by either an (a) or a (b). The fact they are also letters is a red herring you just need to note that it’s one of two values.

The only information in the visitor book that comes in pairs is the entry and exit dates. And there are enough rows to account for letter A-Q.

So just take each number as follows.

O(a) = 2, Q(a) = 15, C(a) = 12, R(b) = 5, J(a) = 25, D(b) = 14

Then you simply convert each number in a letter according to its ordinal position in the alphabet.

2 = B, 15 = O, 12 = L, 5 = E, 25 = Y, 14 = N

The answer is BOLEYN.