Unlike Vienna in Measure for Measure, fornication wasn't punishable by death in Shakespeare's England, but some people wanted it to be. Uptight Puritan extraordinaire Phillip Stubbes (the guy who thought the theater was "evil") wrote that anyone guilty of prostitution, adultery, whoredom, or incest should be made to "taste of present death" or be branded "with a hot iron on the cheek, forehead, or some other part" so everyone would know how sinful they were. Yikes! (source: Anatomy of Abuses, 1583)
On November 28, 1582, Shakespeare was married to Anne Hathaway, who gave birth to Shakespeare's first child, Susanna, about six months later. Hmm. It's a good thing Shakespeare wasn't subject to the laws of his fictional Vienna.
In Promos and Cassandra (1578), Shakespeare's main literary source for Measure for Measure, the heroine who corresponds to Isabella's character sleeps with a corrupt judge in order to save her brother's life.
Literary scholar Jonathan Bate suggests that Shakespeare may have been related to Isabella Shakespeare, an abbess of a nunnery near Stratford-upon-Avon (source). If this is true, does the abbess have anything to do with the Isabella in Measure for Measure?