Gamma detectors at border crossings are intended to detect illicit nuclear material. One of their performance challenges is the fact that vehicles suppress the natural background and, thus, potentially reduce probability of detection of threat items. Here we test several methods to adjust the detection to background suppression in the context of signal estimation. We show that, for the small-to-moderate suppression magnitudes, suppression adjustment leads to higher detection probability. However, for signals triggering alarm without an adjustment, adjustment does not improve estimation of the signal location, only moderately improves estimation of the signal magnitude, and does not improve estimation of the signal width.