Sign Hill Park has several trails leading to the big concrete letters forming the SOUTH SAN FRANCISCO THE INDUSTRIAL CITY hillside sign.
The Ridge Trail runs above the sign along the crest of Sign Hill from Ridgeview Court (where there is a small parking lot) to Spruce Avenue. At the water tank, you can descend below the letters on Letters Trail which leads down to the park entrance on Poplar Avenue. You can complete a loop back up to the Ridge Trail by continuing on either the Iris Hill Trail or the slightly longer Seubert Trail. Depending on route, the total loop is around 1.5 to 2 miles (or 2.4 to 3.2 kilometers).
The hike is relatively easy but does have some steep sections so may not be suited to very small children. The trail loop can also be started from the base of the hill at the Poplar Avenue entrance. From there you can also do a there-and-back hike of just the Letters Trail up to the sign without completing a full loop if preferred.