For uppercase, the tip offs are the following:
* The capital A in Helvetica is narrower (more isoceles and less equilateral)
* The capital G has an extra hatch on the right side (looks like an arrow and not an L)
* The capital R does not have a straight leg in Helvetica
* Conversely, arial chooses a non-straight hatch mark for the Q whereas Helvetica's Q hatch is straight.
This image provides a good overview on the capital (and numeric) differences: http://cdn.ilovetypography.com/img/gqr.gif
In the case of TOYOTA where it seems that kerning might different in two images, the heavier strokes in Helvetica should tip that off.