If your employer still has not signed a written labor contract with you after you have worked a full month, you can claim double wages from the second month on, for up to 11 months; if it still has not signed after a full year, it counts as having signed a contract with no fixed term

In plain words

If the employer has not signed a written contract with you once you have worked a full month, from the second month on it owes you one extra month's wage for each month, up to 11 extra months. If it still hasn't signed after a full year, it is treated as if a contract with no end date had been signed. Sign when your employer hands you the contract; if you deliberately drag your feet about signing, you won't get this money.