The ornamental design for a signaldetector, as shown and described.
FIG. 1 is a front elevational view of a signal detector showing my new design;
FIG. 2 is a rear elevational view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a top plan view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a perspective view thereof;
FIG. 8 is another perspective view thereof;
FIG. 9 is a front elevational view in the state of use; and,
FIG. 10 is an enlarged view of portion 10 shown in FIG. 9.
The long dash-short dash broken lines depict the bounds of the enlarged view of the status display screen and do not form part of the claimed design. The dash-dash broken line depict portions of the signal detector that form no part of the claimed design.