Quoting Brad Abrams in the excellent Framework Design Guidelines:
...I have heard every possible excuse for violating these naming
guidelines. [...] For the most part, our customers have seen the
places in which we have diverged from these guidelines (for even the
best excuse) as warts in the Framework.
In other words, do as they say, not as they do. :)
Also, 'Db' is an abbreviation, not an acronym. Database is one word. Abbreviations should never be used in identifiers per the Guidelines. ('Id' is a special case.)
Sadly the CA1709 link lists 'DB' as an example. :(