The ornamental design for the decorative score keeping device, as shown and described.
FIG. 1 is a front perspective view showing a decorative score keeping device;
FIG. 2 is a side view of the decorative score keeping device of FIG. 1;
FIG. 3 is an additional side view of the decorative score keeping device of FIG. 1; and,
FIG. 4 is an enlarged front perspective view showing the decorative score keeping device of FIG. 1.
The broken line showing of an image depicted in FIGS. 1-4 is for the purpose of illustrating environmental structure and forms no part of the claimed design.