If you look on wikipedia, when a source is cited for a statement in the body of an article, the source is linked to by a number enclosed in square brackets, like this >>[1]. The only other two ways to 'enclose' this link to make it stand out ar parentheses and curly brackets. Both of these options already have standard uses.
Parentheses are used within a text in order to 'bring up' something closely related to what's being presented. Like another way of saying, 'by the way'.
Curly brackets are used extensively in mathematics. Especially in set theory.
Which leaves square brackets to highlight the link to a source.
In the logo for RationalWiki, I see two sets of square brackets. What this says to me is that they're trying to convey the idea, (subliminally), although there may be an external source for something, the real source, the 'trusted' source, is in reality your own brain. i.e. rational thought.
I'm not saying that there isn't some other reason for using square brackets in this logo or the aussie bar logo, there may well be. What I am saying is that people learn things by associating the new stuff to some old stuff. We make connections between ideas by associating one idea to another idea bc of some basic concept that's related to both of them.
As far as the aussie bar logo, if we compare it side by side to the rationalwiki logo, I see the words inside the square brackets representing the two sides of the brain. The left side of the brain processes information linearly, rationally. In the logo the word on the left is upside-down, as if to say take logic and turn it upside-down. Evil is good and good is evil, etc. It's also written in white so, what's the opposite of white?
The right side of the brain processes information emotionally. The word on the right is red. Red is associated with blood, fire, and the devil, but it's also used to represent the color of a heart on a valentines day card, and it's the color of passion. This most basic of emotions can be positive or negative depending on how we control our emotional responses with our intelect. Let's not forget that alcohol dulls the our ability to think rationally. So it appears as if this logois saying, go in the bar, drink some booze, and set your emotions on fire.
Put them both together and you get: Forget logic, turn it upside down and let your negative emotions take over.