punctuation - Is it proper to use a colon followed immediately by a hyphen?

I have seen some writing where people have a list or a figure in writing and they will write something like this:

The information is provided in Image 3:-

Is that correct? Is this a British style?

Answer

According to Nick Marten's The Secret History of Typography in the Oxford English Dictionary, a colon followed by a dash is a typographical mark that the OED refers to as the dog's bollocks:

Citing usage from 1949, the OED calls this mark the dog’s bollocks, which it defines as, “typogr. a colon followed by a dash, regarded as forming a shape resembling the male sexual organs.” This is why I love scrounging around the linguistic scrap heap that is the OED. I always come across a little gold. And by “gold,” I mean, “vulgar, 60-year-old emoticons.”

Marten does not further elaborate on its purported usage, but others do:

In Britain the exclamation mark is sometimes referred to as a dog’s prick, and that, further, the combination of a colon and a dash (:—), out of fashion now but long used to represent a restful pause, is known as a dog’s bollocks.

Modern style guides seem intent on banishing its usage to history. For example, the University of Sussex has a strong opinion on the matter:

The colon [is] never preceded by a white space; it is always followed by a single white space in normal use, and it is never, never, never followed by a hyphen or a dash — in spite of what you might have been taught in school.

I'd love to find some examples in print, but as you can imagine:— it's extraordinarily difficult to google.