I claim the ornamental design for an arm support device, as shown and described.
FIG. 1 is a perspective view of an arm support device, from the front and top.
FIG. 2 is a perspective view thereof, from the rear and bottom.
FIG. 3 is a front view thereof.
FIG. 4 is a rear view thereof.
FIG. 5 is a left side view thereof.
FIG. 6 is a right side view thereof.
FIG. 7 is a top view thereof.
FIG. 8 is a bottom view thereof.
FIG. 9 is a front view of a user wearing the device; and,
FIG. 10 is a rear view of a user wearing the device.
The broken line showing of an arm support device is for the purpose of illustrating portions of the device that form no part of the claim. The broken lines illustrating the human form in FIGS. 9 and 10 are for the purpose of illustrating environment that forms no part of the claim.