Right now the only real significance (game-wise) of the symbols on the cards are used for the Tactics Modules. Some of them require certain criteria to fill the team member slots. Sometimes it's a "Look 16+, or a Sergeant, or a specific symbol.
Hope that helps.
Feel free to ask any other questions you have.
Some of the tactics modules allow you to team up a Machine Gunner with a MGer Assistant. The result is a pretty powerful machine gun "team". In some cases, allowing the team to shoot each phase wether or not a shoot action is played.