There are markings on the receiver, one from factory 26 (like mine, by the way) will have a triangle with the 26 in it.
Here's a page with examples of what that will look like, among other kinds of markings:
http://www.yooperj.com/SKS-24.htm
Here's a page with examples of what that will look like, among other kinds of markings:
http://www.yooperj.com/SKS-24.htm