Basically, it means that we're not a shadow organization that cloaks all it does in secrecy. Rather, we are a public organization that guards some internal knowledge behind closed doors and cyphers.
I suspect the whole 007-like mystique only arose much later - after it was tasked with protecting the president in 1901/2
1. not-so-fun-fact: Lincoln was assassinated while the legislation to create the USSS was awaiting his signature on his desk
However, what they do and talk about within the lodge is secret.
2B1ask1 is a Freemason slogan: To become a Freemason, ask one about joining.
http://freemasoninformation.com/2b1ask1/
In fact, from the page:
> If you are seeking Membership YOU MUST ASK a Mason or a Masonic Lodge for an application.
Can't very well ask one if the fact they're Masons is supposed to be a secret.
Every government and corporation has a few secrets, but I don't think they're "secret organizations", rather, they're "organizations with secrets".
(OK, I'm kinda secret here, because I'm not going to give anyone my email address. But I don't adopt a pseudonym in the physical world.)