How can I get sued without a signed and written contract?

Actually, you can enter into a contract in many ways without a signed, written contract. The legal key is to unequivocally accept the terms of any offer, which can be done (1) orally ("I agree and will do it."), or (2) performance (You perform as requested by the person offering consideration for same, e.g. a reward offer.), or (3) even by silence, if this is the custom between particular parties (You routinely allow a vendor to leave certain supplies in your shop.).

Although an oral contract is just as valid as a written agreement, there can be real problems proving its existence or its terms, when in dispute. Hint: "An oral contract is as good as the paper it's written on." Or: "It's her word against his." The other significant difference between oral and written contracts in California is that the time to sue for breach of an oral contract is shorter, i.e. two years, rather than four years, for written contracts.

There are some exceptions in California (the biggest being real estate transactions) of contracts that cannot be enforced without a writing.  See, California Civil Code section 1624.

IMPORTANT DISCLAIMER: The above material does not constitute legal advice and should not be relied on. It does not create an attorney-client relationship. Each locality has differing laws. A legal matter cannot be satisfactorily resolved without a comprehensive review and analysis of all the unique facts and laws at issue by an able attorney. Your matter may result in a loss of rights if you do not timely retain such an attorney. For more information, please visit: http://www.BealBusinessLaw.com