4 Triangles pointing up (corners) helps you date the card which is from 1904 to 1918.
This postcard also uses the mask system where a template is placed on top of the photo. The Post Office did require a few rules as to the printing of these personal family postcards.
This post is more of an excuse to show off the pretty pictures, point you to them at auction, and link over to a helpful resource.
This will not work if the postcard has been mailed and the stamp box is covered.
This particular postcard is an AZO postcard produced by Eastman Kodak. The triangles, diamonds indicate years of printing.