Legal Question in Real Estate Law in California

Not always. The easement could have been granted by one to the other property. If it is recorded with the county, it would appear on the title report when property is sold.

No. Easements can be created, or come into existence, in about ten different ways, only a few of which require any signature, much less signatures of both. Further, many easements are created long before the current owners acquire the properties that are subject to the easement, either as the holder of the easement rights or the owner of the parcel subject to the easement.

Most easements or apparent easements between two homes that have been used consistently over a period of time will be upheld by the courts, without regard to the existence of a signed agreement.

No. Easements are usually created by a grant from one person to another (one signature) or a reservation of an easement at the time of a sale (one signature). They also arise in other ways, as pointed out by Mr. Whipple. (Some of which do not require a signature.)