Besides the fact that to run a pre 2005 ECU on your car you would need a conversion harness, which hooks into the ECU(its easy to see if looking at the ECU), as the conversion harness is a bunch of blue wires hooked onto all your factory wires and the ECU

In most cases a reflashed ECU would most likely have a sticker on it sometimes, but if it is stock, then the chances of it being a Hondata reflash is very slim, The stock rev limit is 8300 and its hard to tell up that high exactly were your limiter is at, but a reflash would run a bit higher rev limit at 8600..

The biggest tell tale would be your VTEC enguagement point, as the Reflashed ECU's use a floating VTEC point instead of a fixed VTEC point(stock) The floating VTEC is activated by your intake manifold pressure or throttle position. Stock VTEC is set at 5800, so if the car seems to activate below or before 5800rpm's it very well could be a reflash. The VTEC window is set between 4900-5800rpm's with the Hondata reflash, and raises is some situations in order to increase power and add some extra fuel saving features when used on the highway under part throttle or in higher altitude area's....