Baseball cards have been collecting and trading cards for decades that depict players and include stats and facts about their careers. One of the most fundamental pieces of information found on any baseball card is the player’s uniform number. While numbers were originally assigned haphazardly, they have taken on deeper meanings in some cases throughout history.

Most modern baseball teams assign uniform numbers based on the player’s position. For example, catchers usually wear numbers in the high 20s or low 30s. Pitchers tend to wear numbers in the 40s-60s. Infielders usually sport single-digit or teens numbers. Outfielders occupy the teens and 20s. There is no official numbering system and some players wear numbers outside these unofficial positional guidelines.

Originally, numbers were assigned arbitrarily and sometimes changed frequently as players were traded or new players joined teams. The first number formally retired was Yankee Lou Gehrig’s #4 in 1939 after his tragic death from ALS. Since then, retiring numbers has become a way for teams to honor legacy players. Numbers of superstar players that played their whole careers with one team like Mickey Mantle’s #7, Ted Williams’ #9, and Cal Ripken Jr.’s #8 have been retired.

Some players attribute special meaning to their uniform numbers too. While with the Chicago Cubs, Billy Williams wore #26 to represent the letters of the alphabet for his initials BW. San Diego Padres first baseman and Hall of Famer Tony Gwynn wore #19 because as a young fan that was the number his childhood hero, Dodgers star Willie Davis wore.

Individual digits in baseball uniform numbers can sometimes have deeper significance too. One being the legendary #42 that was retired across all of MLB in 1997 to honor Jackie Robinson breaking the color barrier. The single#7 is statistically the most commonly worn number in baseball history likely due to its association with good luck across many cultures worldwide.

Other baseball numbers have taken on historical meaning linked to the timing of significant career milestones. For example, #3 was the uniform number Roberto Clemente wore when he recorded his 3,000th career hit. #51 was the number Roger Maris wore when he broke Babe Ruth’s single season home run record hitting #61 dingers in 1961. #515 was the number Nolan Ryan wore when he notched his 5,000th career strikeout.

While many players today let luck or coincidence dictate their uniform number selection early in their careers, superstitions and personal meanings become attached to their numbers once success is achieved wearing them. Jim Abbott only allowed one earned run while wearing his lucky #44 jersey during his no-hitter in 1993. Likewise, Mariano Rivera’s #42 took on iconic status as the number he wore for nearly his entire Hall of Fame career as baseball’s greatest closer of all-time.

While originally randomly assigned, uniform numbers in baseball have developed additional significance and meaning beyond just identifying players. Individual digits and full numbers have become symbols to remember legendary players and career milestones linked to the numbers iconic stars achieved greatness while wearing. Going forward, we can expect new numbers of today’s best players to take on historical meanings of their own to be remembered for generations of baseball fans to come. The simple numbers on the front or back of a baseball jersey end up representing so much more about the players who made them part of baseball’s fabric.