Though there were some earlier sets, the first important movie star sets were issued in the early 1920s by the American Caramel Company. Two sets were issued, each containing 120 cards. The set designs mirrored the company's two big baseball card sets of the same years. Despite being in black and white, these sets are very nice and show most of the big stars of the era.
Probably the nicest set of the 1930s was the Shelby Gum set (R68), which featured 40 very pretty color cards. These scarce cards are highly prized by collectors, and are very expensive. Even the lesser known stars often sell for $10 a card, and big name stars can sell for $50 to $100 each.
In the late 1940s and 1950s, Topps and Bowman issued some movie star cards in their gum packs. Bowman issued a Movie Star set in 1948, and a pair of Television and Radio Stars of NBC sets in the early 1950s. Topps issued Hit Stars, and Who-Z-At Star sets in the 1950s. Cards from these sets are all fairly hard to find today and on the expensive side.
There were some other types of cards being issued in the early years of the movies, including Dixie Lids, Exhibit cards, Strip Cards, Weight Machine cards, and Movie Theatre cards.
Dixie lids are circular cards that are actually the package lid that came with little ice cream cups. These cards have a tab where the lid was removed from the cup. They were issued from the early 1930s through the 1950s. Collectors had the choice of keeping the lids or returning a bunch of them for a big rectangular card of the star. The big cards are called Dixie Premiums. While interesting and scarce, Dixie lids have never been widely popular because of their odd size and lack of color.
Exhibit cards are postcard-sized, thick, black and white cards that were sold for a penny apiece in arcade machines. They were issued from the early 1920s through the 1960s. Their big size and lack of color has hurt them in collector popularity, but these are some interesting cards and they are generally more available than most early American movie cards.
No, strip cards are not X-rated, they got that name simply because they were issued in long strips instead of as individual cards. Strip cards are usually found cut apart, though they are sometimes found in complete strips. The quality of the cut in strip cards varies widely, from careful trimming with scissors to a quick rip with the hands. Strip cards usually feature crude color or black and white drawings, though they are sometimes photographic. When issued, these were usually sold in a strip of 10 cards for a penny, so the cardboard quality and artwork were usually subpar. Strip cards are almost always found with blank backs, and usually do not give any indication about who issued them.
Weight machine cards are small thick cards that came out of weight machines. In the days of penny arcades, people could stand on a weight machine, insert a coin, and receive a card. The card would show a movie star or some other subject on the front, and the back would show a printout of the person's weight, along with the date and a fortune. Weight machine cards usually have black and white photographic artwork of somewhat low quality.
Movie Theatre cards are cards that were given directly to movie theatre patrons at some theatres. Theatres would give out a different card each week, often showing a list of upcoming films and their screening dates on the back. These cards are very rare, since they were distributed at only one theatre in the country. These cards vary in size, but are often found postcard-sized. There are some very beautiful cards that fall into this category.
For some of the American card sets, a catalog number will be listed for the set (examples: E123, R68, W512, etc.). These numbers come from the American Card Catalog, a book written by Jefferson Burdick and last updated in 1960. Burdick catalogued just about every American card set from 1879 to 1960 in this book and assigned them numbers. Even though the book itself is little-used by today's collectors, these catalog numbers continue to be used by collectors to identify many card sets.
All in all, collectors of American movie star cards must be willing to accept cards of mixed quality at fairly high prices. Just about all American movie cards are on the rare side, making them difficult to find, but making a collection of them unique from most other collectors.