Santa Cruz — Sign postings leading to the surf of Cowell Beach, just west of the boardwalk, ban all the usual transgressions: diving, fires, litter, smoking, feeding the birds and sea lions. The group’s annual report card of beaches doesn’t look at trash on the sand — for which Cowell wouldn’t be the biggest offender — but at the level of fecal indicator bacteria, microorganisms naturally found in the human gut, whose prevalence in the water suggests the presence of other pathogens.