Larry is right, it's the personal "a". It's used to introduce the Direct Object of a sentence when this object refers to an individual, a group of people or a pet. There are lots of other rules and exceptions, but this is the basic rule.
Obedezco las reglas (I obey the rules).
Obedezco A mi padre (I obey my father).
¿Has visto esta película? (Have you watched this movie?).
¿Has visto A Marta? (Have you seen Marta?).
I hope it helps. If you have any questions, feel free to ask!