Merchants in a downtown Oakland district have organized a campaign telling shoppers"please say no" to panhandlers. Members of the Lake Merritt Business Assn. have put signs in their windows urging people not to give to beggars and, "instead, support community services designed to help the needy." Walter Harmon, owner of a restaurant and bakery, said he started the campaign because his customers were constantly being harassed. "I've chased them. I've used my stun gun, and I've handcuffed them," he said of the beggars. "I've personally made 50 to 60 citizen arrests. I've done everything, but it hasn't really helped."