How is a miner prevented from adding transactions without signatures to their block? Consider I'm a miner. I mine on my own, I don't mine in pools. I have power enough to find the hash, lets say, once per 2 years.

When I find the hash within those 2 years I send the block back to the network and since the hash is low enough the block would be accepted and added to the block-chain.

It's up to miners (so me) to check the transaction signatures but the block AFAIK doesn't contain the signatures. How can others within the network can be sure that all the transactions in my block which I calculated were signed? 

If I was an evil miner, I could have added a transaction without a signature. How is this prevented? Am I the only one who checks the signatures within my block?

Thanks for explanation.
No, you're not the only one who checks signatures.

Before a block is submitted, every signature / transaction is checked/verified by other nodes.

I believe the SHA256 hash is the first thing which they check, which contains all/most headers for the block.Then every tranasaction hash +/signature is checked.

If they can't confirm a transaction hash / block hash i believe your block will be rejected.

This might help you out a bit, -> https://en.bitcoin.it/wiki/Protocol_rules#Explanation_of_Some_Rules