If Gov. Jerry Brown signs legislation known as the Trust Act, federal immigration authorities will have a somewhat harder time taking custody of people in local jails who are suspected of being in the country illegally. The measure, which would prohibit local jailers from holding most arrestees for an additional 48 hours before federal authorities arrive, is not expected to put a large dent in the number of deportations. But with a revamp of immigration laws stalled in Washington, immigrant rights advocates hope to send a message that most deportation should end. Along with a bill granting driver’s licenses to more immigrants who are in the country illegally, the Trust Act would cement California’s position as one of the states most hospitable to such immigrants.