As a verb (past tense):
* The artist signed her name on the bottom of the painting.
* The peace treaty was signed by both countries.
* She signed up for the marathon last week.
As an adjective:
* The signed baseball was a valuable collector's item.
* The contract is signed and binding.
* He gave me a signed copy of his book.
In different contexts:
* Signed language is used by people who are deaf or hard of hearing.
* The musician signed a record deal with a major label.
* She signed the check and gave it to the cashier.
Using "signed" with prepositions:
* He signed up for a cooking class.
* The document was signed off on by the manager.
* They signed on to the project with enthusiasm.
Remember that the context of the sentence will determine the exact meaning of "signed."