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davidcyclebackMost to all of the digital/computer reprints will have a multi color dot pattern throughout the whole sign. The original may have areas of dots, such as with the player image, but will almost always have large areas of solid color.
Those reprint tin signs may have areas of solid color, as the were professionally made-- however, they're metal and plentiful on the market.
For a Pre-WWII sign or poster, if you have a strong microscope and see dots of magenta ink in the multi color half tone dots, it's a reprint. Magenta is similar to a dark pink or purplish-pink. Magenta, as opposed to traditional blood red, for halftone color dots was used after WWII. Duly note that it should be an isolated dot of ink being magenta, rather than overlapping dots. Overlapping dots can create various colors (blue + yellow = green, for example), and it is the individual ink (isolated dot on ink) that must be magenta ... Similarly, if you see a halftone print with isolated (no overlapping) red ink dots, it's vintage, as red ink was only used Pre circa 1950.
However, from a practical standpoint, almost no Pre-WWII baseball cards and little Pre-WWII memorabilia has color halftone printing (multi color dots). I've seen Pre WWII magazine covers and inside pictures that are color halftone, but that's about it. So a multi color dot pattern on a 1910 baseball card or 1915 ad sign typically identifies the item as a reprint. If you find a Christy Mathewson Tuxedo Tobacco Sign and the print has a multi color dot pattern throughout the whole sign, it's a reprint.