There are multiple settings that allow you to control how duplicates signals for a single symbol are handled in aggregate and per strategy.
The first setting is on the Settings tab in the main robot window. It controls whether to trade duplicates signals in the same symbol across all strategies. Note that this setting does not care whether you were actually filled on a trade that was sent from the robot - only whether a signal was received.
The trading robot will not take a trade in a symbol IF there is already an order in for that symbol or if there are already holdings in that symbol.
If the robot has already taken a trade in a certain symbol today and the position is now closed, by default the robot will take trades for signals that it sees in that symbol after that point.
This would allow the robot to take multiple round trip trades in the same symbol.
If you'd like to disable this behavior and only allow the robot to trade a specific symbol at most once in a day, enable this checkbox.
There are per strategy settings as well that determine the robot's behavior. On the edit strategy form, you'll see the following settings:
The Trade a symbol at most once per day for this strategy setting says that for this strategy alone only trade a given symbol once per day.
The Send order even when holdings exist for symbol says that duplicate signals will be traded even if you already have a position in the same symbol.