An external physiological sensor probe in which a transducer responsive to in vivo physiological signals is placed in an appropriate position on the body. The transducer is mounted in a housing to permit placement of the transducer next to the skin or in contact with the skin if necessary. A marker member or element is slideably mounted on the transducer housing and resiliently urged to a position distal of the transducer. The marker member acts as a handle and may be placed in contact with the body upon application of a certain predetermined force. The marker member produces an indication on the body as to the position of probe as well as its alignment thereby enabling its positioning in the exact same location at a remote time.