IIRC:
The assumption is everything is simple - just highs and lows with the wind blowing around them.
Draw a little diagram with one high and one low, wind blowing clockwise around the high and anti-clockwise around the low.
If you are flying E->W with wind from the N (right) you must either be approaching a high or leaving a low.
Another assumption is you are holding a steady indication on your Altimeter. So using:
High to Low: Watch out below
Low to High: Safe up in the sky
you will be climbing.
OC619