As seen in the picture up above this would be a time signature which would tell how the beats of the song would be and how the notes in the music will look.
While in this image it shows what will happen to any notes that are on that line of the measure, there are even times in which the one of these signs will only be there for a specific measure which would cause the note to go back to playing neutral after the measure or if the neutral sign is put on a later note that is the same as the sharped or flatted note.
Images up above belong to pianomother.com