This tiny republic is issuing four postage stamps dedicated to the fight against AIDS, the government said Thursday. The stamps, due to come out in the next few days, were prepared in conjunction with an international congress on AIDS in San Marino in October. ``The set carries a warning but at the same time hope,'' a government statement said. The stamps cost about 18 cents to 71 cents each. San Marino, an enclave in Italy's Apennine mountains, claims to be the world's oldest republic, founded in 301. Tourism and its postage stamps and coins are its chief sources of income.