The first thing you need to look for is is and H or an L stamped somewhere near the serial number.  High pitch horns are not playable with other instruments tuned to modern standards. and they never have much value.

The P in the serial number indicates that it was made for sale as a merchandiser-branded horn, otherwise known as a "stencil" horn.  Stencil horns were watered-down versions of the horns manufacturers sold under their own brands.  The C might indicate that it is in the key of C rather than the usual Bb.  There are no good records of manufacture dates tied to Conn stencil serial numbers.  Stencil horns were a big market in the 1910s - 1920s, so your horn is most likely based on a Conn New Wonder, either Series 1 or Series 2.  The later horns were much improved.  

Conn made some very good and highly sought-after sopranos in the 1920s, but their stencil horns are not nearly as valuable as the ones sold under the Conn brand.  Yours might be roughly equivalent to a Pan American (Conn stencil) in value,  The biggest variable would be condition.

The information and photo gallery on saxpics.com might help you get an idea which Conn soprano yours is based on.