  The GRANDProto300 (GP300) array is a pathfinder for the Giant Radio Array for
Neutrino Detection (GRAND) project. Serving as a test bench, the GP300 array is
expected to pioneer techniques of autonomous radio detection including
identification and reconstruction of nearly horizontal cosmic-ray (CR) air
showers, and shed light in understanding the interesting `transition region'
from the galactic to extragalactic CR sources. An offline analysis of signal
identification over ambient noise is crucial at this stage, where very relaxed
self-triggering thresholds of radio antennas will be used for study purposes.
In this work, we show results and efficiency of signal identification with
classical approaches using a wide set of simulated realistic signal templates
and also validated against measured background recorded by deployed prototypes.
