Cut your cardboard base to the desired bookmark size. Then trim two music sheet rectangles to match the size, leaving a small edge for sanding later.
Apply a thin, even layer of Mod Podge to one side of the cardboard and carefully press the music sheet onto it, smoothing out any air bubbles. Repeat on the other side.
Once dry, lightly sand the edges to blend the paper into the base. To give it a vintage touch, brush a bit of brown paint or distress ink along the edges and corners.
Seal the surface with another coat of Mod Podge or clear spray for durability. Punch a hole at the top center and insert your tassel. Now, add a charm or bead for a decorative accent.