“Bravo sierra” means, using the phonetic alphabet, the letters “B” and “S,” and stands for the words “bull shit” (or “bullshit”). “I think this is a far more honest feeling than the Bravo Sierra being spewed into the public mind by men like Edward Kennedy” was printed in The Morning Call (Allentown, PA) on October 14, 1969. “The errata and “bravo sierra” so far outweigh the honest moments that reading the book is often a painful and embarrassing experience” was printed in the San Diego (CA) Union on July 12, 1981. Both “Bravo Sierra” (upper case) and “bravo sierra” (lower case) have been used.
 
“I call Bravo Sierra” means “I call bullshit.” “I call bravo sierra” was entered in the Urban Dictionary on October 14, 2006. “I call Bravo Sierra. Lemme see a biz card with that title” was posted on Twitter by Michael Montgomery on August 7, 2008.

 
   
Wikipedia: NATO phonetic alphabet
The NATO phonetic alphabet is the most widely used radiotelephone spelling alphabet. It is officially the International Radiotelephony Spelling Alphabet, and also commonly known as the ICAO phonetic alphabet, with a variation officially known as the ITU phonetic alphabet and figure code.
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The 26 code words in the NATO phonetic alphabet are assigned to the 26 letters of the English alphabet in alphabetical order as follows: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.
   
21 April 1952, Boston (MA) Traveler, column by Bob Sibley (Aviation Editor), pg. 30, col. 5:
AH. ROMEO—That new internation phonetic alphabet is now officially in use in aviation communications, putting such terms as “Uncle Victor William” out of business in favor of “Union Victor Whiskey.” Just call me “Bravo Sierra” instead of “Baker Sugar.”
 
Newspapers.com
14 October 1969, The Morning Call (Allentown, PA), “Public Opinion,” pg. 16, cols. 4-5:
I think this is a far more honest feeling than the Bravo Sierra being spewed into the public mind by men like Edward Kennedy.
(...)
Louis Cerullo
105 Parkway Road
Allentown
     
12 July 1981, San Diego (CA) Union, “Truth and Lies,” Books sec., pg. 4, col. 1:
The errata and “bravo sierra” so far outweigh the honest moments that reading the book is often a painful and embarrassing experience.
 
Google Books
Fast Jets 2
By Chris Allan
London, UK: Osprey
1987
Pg. 36:
This is where the Bravo Sierra stops — irrespective of rank and experience the scores tell all.
 
Newspapers.com
17 November 1993, Tallahassee (FL) Democrat, “Your Letters,” pg. 10A, col. 3:
Vietnam Vets have had to put up with a lot of Bravo Sierra since we came home.
(...)
Niel W. Christensen
Public Affairs Director
Big Bend Chapter 96
Vietnam Veterans of America
 
Urban Dictionary
I call bravo sierra
Bravo and Sierra are two of the military’s words used to prevent misunderstandings in radio transmission. They stand for the letters B and S in the same way that Alpha means A and X-Ray means X.
Using “I call bravo sierra” is a more articulate and less crude way of saying “I call bullshit”. It also can be a coded way of letting your friends know what you think while keeping the clueless out of the circle.
The phrase has been popularized by the XM Satellite radio team of Opie & Anthony.
(...)
by Chris Zizzo October 14, 2006
 
Twitter
Michael Montgomery
@Montgomery
Replying to @davidnbrooks
@luzcannon I call Bravo Sierra. Lemme see a biz card with that title.
2:18 PM · Aug 7, 2008·Twitter Web Client
 
Twitter
⚾️ BostonWriter ⚾️
@bostonwriter
@captcutoff - I agree 100% Sincerity? Humility? Genuine emotion? I think not. I call Bravo Sierra.
11:41 PM · Aug 26, 2008·Twitter Web Client
 
Twitter
PhilosophyGuy
@PhilosophyGuy
Is it just me or does David Blaine look too well rested to be up 60 hours hanging upside down…  I call “Bravo Sierra” !!!!
11:12 PM · Sep 24, 2008·Twitter Web Client