EURUSD.FXCM is probably the symbol you want.
I say "probably" because FXCM is the data provider that the "Forex - Basic" data subscription includes. If you have the "Forex - Premium" data package, this will include the Tenfore providers. which have their own contributor codes like .ABBA, .BNPF, etc. See http://www.iqfeed.net/symbolguide/index.cfm?symbolguide=guide&guide=forex&symbolguide=guide&type=TENFORE
for a list of how these codes work.
If you built the indicator yourself in NinjaTrader, you should get the same results outside of it as long as you use the same symbol (include the same .FXCM contributor code) and the same other factors. Beyond that, I'd need to look at the indicator more closely to try and suss out the difference.
DTN IQFeed Implementation Support Specialist