That's not exactly true.
Property deeds document property ownership and transfer. That is their purpose. The original is usually signed. Any other information that they contain is usually to clarify the property ownership or transfer. There may be extraneous information as well if the individual drafting the document believed it was necessary.
Death Dates
It is always possible that a deed may state the day on which the owner died, but it's not all that common. If the deed is transferring property from the estate of someone who is deceased, the date of the deed can be used as "dead by" date--as long as the owner is listed as deceased. Sometimes if a wife survived her husband and had a "life estate" in her husband's property, a deed may be drawn up by the heirs after her death. In cases of this type the widow may not even be named and her death may not even be referenced. It will take a knowledge of the property title she had, often from other documents such as her husband's will or estate record, to know if this type of deed might have been drawn up.
But those deeds provide "dead by dates" more than a precise death date. And other documents may be necessary in order to interpret the deed correctly.
Signatures
The actual deed probably contained the signature of the grantors. The thing is that most local land records are not the actual deed. The deed in the courthouse is a record copy. Before photoduplication techniques were developed in the 20th century, record copies were handwritten or typed transcriptions. They will indicate if the grantor signed his name, but it won't be the "signature" of your ancestor. It will be the clerk's copy of the signature.
Deeds are wonderful records. But, like any record, they need to be analyzed and interpreted correctly.