Do you mean that if you watch the coolant (cold engine, cap off), you see it push out with every compression stroke? If so, that sounds bad. Otherwise, if it's just overflowing as the engine warms up (cap off), that'd be normal as that system needs to to be under pressure.
There are tests to confirm a bad head gasket (which if overheated will mean a warped cylinder head). There's a device called a "Block tester" which is placed over the coolant bottle (cap off) and has a blue liquid in it that's made to change color if carbon monoxide passes through it. If it turns yellow, it's detected carbon monoxide. Another way is to pressurize the system, remove plugs and look into the cylinders for coolant using a very small telescopic light end or boroscope. The block check method's easier by far and any shop that does engine work should have one. The major tool distributors that frequent auto repair shops sell them.