Searching for punctuation in Preview In Preview (v 5.3 on 10.6.8), if I search for a single letter such as k in a pdf, the program will find and highlight every instance of that letter in the pdf.

However, if I search for a punctuation mark such as ? or ;, it will report Found on 0 pages, even when the document is littered with such punctuation.

How can I get preview to search for punctuation? 

The reason for this is that I wish to locate all instances of missing references (denoted as [?]) in a pdf output from LaTeX. 
(Yes, I know that LaTeX will tell me where they are in the source file, but I wish to find them in the pdf.)
A year late but may help others:

For me escaping it in double bracket works so try searching ":" or "?".

Escaping in double quotes searches for whatever is between the quotes similar to the way google does their search options.