The “king of hobbies” is changing. Once the domain of hobbyists trying to complete their collections, stamp collecting has shifted to investors seeking individual collectible stamps worth money.

Only five of these Plate 77 Penny Red stamps are known to exist, and they’re worth more than a pretty penny: One sold for £550,000 in 2012 ($735,850 today), and another sold for £495,000 in 2016 ($662 ...

Collecting stamps is more than just a hobby for many; it’s a gateway into a potentially lucrative world. Among the tiny paper ...