Topps published this stamp set (in sheet form) through boxes of Bazooka gum in 1964. While small in stature at about 1" x 2" each, it's full of stars, from Aaron to Mantle to Yaz. (Not to mention Zimmer; full 100-player checklist at OldBaseball.com.)
Glue-backed and intended for a companion album, they checklist using the upper-left corner number. This is the only #5 I've seen, so I picked it despite having only 8 of the 10 stamps you'd find on a complete sheet. (Norm Cash and Orland Cepeda are the missing pair from its bottom edge, which would've bumped the price significantly.)
Topps published stamps thoughout the 60s and early 70s, with most sets sharing a very similar design. (Compare 1964's sheet to The Topps Archive's profile of 1974's stamps and team albums.)
I've seen dealers and collectors confuse one year with another, so familiarize yourself with a stamp set's design details--mostly name-and-team banner--if you plan to pick some up.
Value: Full sheets list in the 2010 SCD guide for $25 and up, depending on pictured players. Individual commons run about a dollar and stars up to ten.
Fakes / Reprints: Glued backs and perforations make faking a full sheet challenging technically, though not out of the question. (I haven't personally seen any reprints in the market.)