First, it is good Netiquette to include a job title. So, do put your job title. Thus, message is more readable.
Job Title Netiquette Signatures
It follows, work is role play. And so, persons role identifies their responsibility in the company. Knowing what someone does may help a reader understand a message from them. It provides semantics. Meaning attached to data.
Signatures Job Title
Professional email signatures include the role of the author. Providing information about your responsibilities in an organization gives a message credibility. Then, the context of the message. Given, by the role provided. The correspondence is more believable.
Job Title Netiquette
Titles in professional messages because it provides context.