The ornamental design for a safetydevice for an appliance knob, as shown and described.
FIG. 1 is a perspective view of a safety device for an appliance knob according to the present invention;
FIG. 2 is a front elevation view of the safety device of FIG. 1;
FIG. 3 is a cross sectional elevation side view of the safety device of FIG. 2, with the section taken along a longitudinal centerline 3-3 of the device shown in FIG. 2;
FIG. 4 is a front elevation view of the safety device of FIG. 1 shown in a position of being removed from an appliance knob in which the appliance knob is shown in phantom and not part of the claimed design;
FIG. 5 is a side elevation view of the safety device of FIG. 1 shown in a position of being removed from an appliance knob in which appliance knob is shown in phantom and not part of the claimed design;
FIG. 6 is a front elevation view of the safety device of FIG. 1 shown installed on an appliance knob in which appliance knob is shown in phantom and not part of the claimed design; and,
FIG. 7 is a side elevation view of the safety device of FIG. 1 shown installed on an appliance knob in which appliance knob is shown in phantom and not part of the claimed design.
The broken lines showing the knob and appliance form no part of the claimed design.