Although I've already explained what it is that the bat symbol stands for, in detective comics #974, writer James Tynion IV gives a much more simplistic version of what the symbol stands for, “Those that wear it don’t kill. Ever.” (https://www.cbr.com/detective-comics-bat-symbol-true-meaning/#:~:text=Sure%2C%20the%20symbol%20represents%20a,shines%20in%20Gotham's%20nighttime%20skies)
This is Batman’s main moral code.
The one line that he refuses to cross under any circumstance, and he doesn’t take lightly anyone working under him breaking this main rule.
To an extent this could represent a version of the Christian 10 commandments.
The 10 commandments are a set of guidelines for Christians to follow, and while they are not a surefire way to ensure your entrance to Heaven, they are considered to be a good footpath to follow inorder to live your life in a way that God would approve of.
In turn, while playing along with the guidelines that Batman sets out for you may not give you a spot in his good graces, it will mean that he will view you as less of a threat.
Besides killing, which is his number one rule, there are, of course, a few other non-negotiable terms that a partner must be willing to meet if they are to work under the bat symbol.
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He doesn’t use excessive violence, such as torture, in order to get information or to take down a criminal; although in more recent years this rule has been ignored in favour of showing gory action scenes in liveaction film and video games.
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Neither him nor his partners (even though there are notable exceptions -such as Red Hood, Batwoman, and Nightwing during his cop/spy days-), are trained to use guns. A gun was the weapon that was used in the murder of his parents and, as such, Batman doesn’t think too highly of them.
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While he may take the upholding of justice in the city into his own hands, he is never the one to give out punishment to any of the criminals he takes down. He is a firm believer in the idea that he cannot be judge, jury and executioner, and instead leaves this part of the justice process to the law system.