Sling bullets dating from 4th century B.C. have been found with the words "take that" inscribed on them.
Obviously, these aren’t the bullets we have today. The most similar projectiles were rounded stones back then. Some were also made from clay, but the best ones came from lead. Leaden sling bullets were used very widely in the Greek and Roman worlds. Lead is very dense for its size, making it an ideal projectile.
The lead sling bullets were cast in numerous ways and came in multiple shapes, most popularly resembling an acorn. The Latin word for a lean sling bullet is glandes plumbeae, literally leaden acorns. Another common one resembled an almond or an American football.
Symbols were often inscribed on them too. Common ones were lightning bolts, snakes, or scorpions, the point being that they could strike without warning. Some had writing on them instead. Artifacts have been found that have writing on them like “Take this,” “Ouch,” or “For Pompey’s backside.”