The phrase "detectable signs" refers to the noticeable or observable indications or evidence of something. It means being able to identify or perceive signs that can be noticed or observed. Full definition
A heart murmur often is the first detectable sign of heart disease. (epictrial.com)
Currently, skin biopsy is the accepted standard for measuring the loss of small, unmyelinated C fibers in the epidermis, one of the earliest detectable signs of peripheral nerve damage. (sciencedaily.com)
This could be the very first detectable sign of the heartworms. (allstarpetresort.com)