with a Valentine Greeting warm
This old postcard looks like it would be right at home in Tetris or Super Mario Bros. I'm not enough of an art expert to say if this illustration would officially fall under the Cubism movement that began in the early 20th century, but it certainly seems that's the case.
There's no indication of the publisher or artist on the front of back. The only significant things pre-printed on the back are "MADE IN U.S.A." and "Series 514 B." Someone has written "E. Clap?" in pencil, indicating that they think the artist might be the famed and prolific Ellen Clapsaddle (1865-1934), but I can't find any way to confirm if that's true.
The postcard was never mailed, but it was addressed "From Lester Warner" to Howard Pollok in the village of Dansville, Michigan. Dansville is located in Ingham County, and I found a Howard Lewis Pollok of Ingham County who lived from 1909 to 1975. I think it's a good bet that he's the same Howard who received this Valentine. If he was a schoolboy at the time, that would date the postcard to sometime in the late 1910s or early 1920s, perhaps.