The ornamental design for a bicycleseatpost, as shown and described.
FIG. 1 is a perspective view of a bicycle seat post showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is another perspective view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claimed design, while all other broken lines are directed to environmental structure and are for illustrative purposes only; the broken lines form no part of the claimed design.