Does William Petersen really know sign language?

While William Petersen is known for his portrayal of the character Gil Grissom in the TV show CSI, who uses sign language, there is no public information confirming that William Petersen himself is fluent in sign language.

It's important to note that:

* Actors often learn specific skills for roles. While Petersen may have learned some basic signs for his role as Grissom, it's not necessarily indicative of him being fluent.

* Sign language is a complex language. It requires years of dedicated study and practice to achieve fluency, and there's no evidence suggesting Petersen has undertaken this level of learning.

While it's possible he has a personal interest in sign language and has learned some, without official confirmation, it's best not to assume he is fluent.