Daniel is no longer in the mountains serving with Rosh. He's accepted Simon's offer to stay in his house and tend to his forge while he's away following Jesus. But Daniel's still as passionate as ever about driving the Roman occupiers from his homeland. Just because he's no longer a member of Rosh's gang doesn't mean he's given up his subversive activities.
As well as working in the forge, then, Daniel's also conducting clandestine meetings with other zealots. In fact, Daniel takes a lead role in actively recruiting young men about his own age to take on the Romans. It's a highly dangerous activity; if the Romans get wind of what's happening, Daniel and the other young men are certain to be tortured and brutally executed. Under such circumstances, secrecy is absolutely essential.
So too is loyalty. The young men decide that the best way to bind themselves to each other is by devising a password, or code. The sign they use is a bow of bronze, which emphasizes not just their determination to drive out the Romans, but also their firm belief that they are doing God's work. The password comes from Psalms 18:34 which states
He teacheth my hands to war, so that a bow of steel is broken by mine arms. (KJV)
The King James Version uses "steel" instead of "bronze," but other versions do in fact use "bronze," which was more commonly used for weaponry in Judea at that time.