A lot depends on what they are.
Most of what you have scanned appear to be dated precancels with "SRC", which is an abbreviation for Sears, Roebuck & Company, one of the most prolific users of precancels during that period. Furthermore, Philadelphia was one of the most common locations where these precancels were used. (Another common one is "MW" for Montgomery Ward, similiarly very common.)
There are elusive ones out there, however, along with certain typefaces and dates that make some of these dated precancels a challenge to find. However, as it relates to value, most of the "SRC" and "MW" examples are very common and of little monetary value. For a collection, however, they make for an interesting sideline. For more information, I suggest you read this article on the Precancel Stamp Society website:
http://www.precancels.com/US/srcbasics.htm