The ornamental design for a motorcycle fairing supportbar, as shown and described.
FIG. 1 is a front perspective view of the motorcycle fairing support bar;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left side elevation view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a right side elevation view motorcycle fairing support bar in use.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.