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Not sure what you are looking for. I do not know of such a symbol in Appian.
Symbol used for?
Generally for flow chart, we use parallelogram for the input or output fields.
this is what you want to know right?
In a flowchart a parallelogram symbol is used to represent input and output operations. This shape indicates where data enters or exits a process, such as user input or displaying results.
Can you please share the resource link
https://miro.com/flowchart/symbols/