The ornamental design for a tissuelevelindicator, as shown and described.
FIG. 1 is a front peripheral view of the tissue level indicator; and
FIG. 2 is a top view of the tissue level indicator; and,
FIG. 3 is a side view of the tissue level indicator containing a tissue box.
The broken line showing of structural features is included for the purpose of illustrating non-claimed subject matter and forms no part of the claimed design.