ZuluTango4, SierraGolf5 and Cynthiafortune are a trio of rather strange accounts on Twitter. All three post almost nothing but endless streams of numbers, all day every day, with seemingly no human involvement and for no apparent purpose.
None of them have any followed accounts or liked tweets (or at least they aren't made visible).
SierraGolf5: twitter archives
Joined Sept 18 2013. At 375k tweets, it's the most prolific tweeter of the three accounts, though Cynthia is older by a year and a half.
Posts every 6 minutes. Alternates between 5-digit numbers and 5-character capital-letters-and-digits chunks (base 32?), with the switch seemingly happening on the hour. It also posts lines from the Lincolnshire Poacher folk song; these also seem to be posted on the hour but not every hour.
The account seems to have some particular logic regarding what it posts on each hour. Whether or not the "mode" switches, on the hour a tweet will be skipped unless it's a lyric hour, in which case both the lyric tweet and a code tweet will be posted at the same time.
Some archived examples:
10am tweet skipped (no mode switch); 11am tweet doubled as one was a LP lyric post- https://archive.is/dFj5E
9 and 10pm lyric double tweet in letter mode https://archive.is/PGvRc
The only interaction I've yet to see is a lyric tweet and switching mode on the same hour.
The avatar is a device used by number stations. Together with the lyrics, it's a clear reference to the Lincolnshire Poacher number station. This station also used groups of five digits, though I don't think that's exactly a unique thing among number stations.
It has quite a few followers. They seem to mostly be normal Twitter users, likely those curious about the account; many also follow the other two accounts detailed below. Two interesting followers:
An account for an actual, presumably unrelated ARG
An Enigma machine simulator
ZuluTango4: twitter archives
Joined Jan 24 2016. Posts every five minutes, seemingly without pause. It's the youngest of the three accounts and has racked up 175k tweets.
The... rather unsettling avatar is an etching by one Vuminkosi Zulu. As "zulu" is part of the military alphabet, I'd assume the artist was chosen based on the Twitter name rather than the other way around.
Other than that it's... uh... I hate to say "normal", but it's certainly the least interesting of the three. I've seen no variation in activity on it, just endless numbers.
Both Zulu and Sierra post 23 sets of five characters per tweet; this is the maximum amount of 5-character chunks (including spaces) you can stuff into 140 characters.
Cynthiafortune: twitter archives
Joined January 3, 2012. The odd one out of the three, it posts very slowly compared to the other two, and apparently less regularly. Despite being the oldest, it has only 35.7k tweets to its name. Additionally, its tweets only have 22 chunks.
Avatar is an isolated neon light letter c, undoubtedly in reference to the account's name. Banner image, which the other two accounts don't have, is some building that's probably recognizable to some people. It's also the only one without military alphabet in its name.
Speaking of the Lincolnshire Poacher, there's this little story...
http://kernelmag.dailydot.com/features/report/4947/did-we-take-out-mi6s-secret-line/
This site claims to have discovered a phone line transmitting messages in the format of the Lincolnshire Poacher, and to have subsequently gotten it shut down by calling attention to it. Oops?
It's unclear whether the site was taken on a ruse cruise, the site is taking its audience on a ruse cruise, or the whole event is entirely legit. At any rate, this all happened in early September of 2013... Right before the creation of SierraGolf5. HMMM.
Additionally, the name of the "backup channel" given, "romeo x-ray three nine", is similar in format to Sierra and Zulu's account names. There doesn't seem to be a twitter account under any variant of that phrase, though it's hard to verify because there's multiple ways "x-ray" could be formatted.
This thread has more comments from the author with some additional tidbits, people haggling over how legit this is, and an additional recording from the same(?) number- look for the "daniel-case" soundcloud links.
So, can we crack it?
Most likely not. If the accounts follow the same format as the original number stations, the messages most likely use a one-time pad, which makes them nigh uncrackable without said pad.
There are cases where one-time pads have been cracked outside of finding the pad, but it usually requires a gaffe on the part of the one sending the message, such as recycling a pad or ending every single message with "heil hitler". Without any context or any idea of what the messages are supposed to be, these methods are useless.
Additionally, regardless of the encryption method used, the Twitter format itself and the sheer volume of messages means the vast majority of messages are just plain buried by now. Even if each tweet, or each manageably small sequence of tweets, was a stand-alone encrypted message, you'd really have to go digging to get at any of the older ones. As such, the deeper hidden meaning of the Lincolnshire Poacher twitter accounts is beyond our reach.