means wherein the elongated element includes an extension arm with visible means on the outer extremity and a weight arm which preferably includes a spring assist adapted to rotate the boat trailer marking device into vertical position for marking and tracking the movement and location of a boat trailer from a towing vehicle and for gauging the depth of the water when the boat trailer is in position on a boat ramp for loading a boat and for locating and targeting the center of the submerged boat trailer while loading the boat application_number US 25436594 A description in the detailed description like reference numbers are used to identify the like components in each of the figures fig1 shows boat trailer 10 with trailer rails 11 and a pair of boat trailer marking devices 12 secured in place on boat trailer 10 with elongated element 14 in an activated vertical position such as occurs after a boat not shown has been removed from boat trailer 10 elongated element 14 includes extension arm 16 and weight arm 18 with weight attached thereto in an alternative embodiment elongated element 14 may be of one piece construction mounting device 22 is shown attached to axle 24 of boat trailer 10 but mounting could also be achieved on a portion of the trailer frame or rails skids or bunks a boat trailer with one or a plurality of marking devices of the present invention operates in the following manner when a boat is loaded onto a trailer the marking devices are rotated down or forward and.