The ornamental design for rail guard for baby carriage, as shown and described.
FIG. 1 is a front perspective view of a rail guard for baby carriage showing our new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is bottom plan view thereof;
FIG. 5 is a right side elevational view, the left side being a mirror image thereof; and,
FIG. 6 is a perspective view showing the present invention applied to a baby carriage. The baby carriage and the bottle are shown in broken lines for illustrative purposes only and form no part of the claimed design.