I claim the ornamental design for a single patient lift strap device, as shown and described.
FIG. 1 is a front perspective view of a single patient lift strap device.
FIG. 2 is a back perspective view thereof.
FIG. 3 is a front view thereof.
FIG. 4 is a back view thereof.
FIG. 5 is a bottom view thereof.
FIG. 6 is a top view thereof.
FIG. 7 is a left-side view thereof; and,
FIG. 8 is a right-side view thereof.
The broken lines seen in the drawings are included for the purpose of illustrating stitches on the single patient lift strap device and form no part of the claimed design.