Great info Wojtek! Thanks mate!
I started scribing my models too not long ago, and use a cut down metal venetian blind and a normal metal workers scriber. I like Wojtek's idea of using a pin, as the panel line would be a bit thinner (and more 'in-scale' ) than those done with the scriber tip.
The good thing with the metal venetian blind is it's very thin aluminium, so it's light and flexible, and looking end-on, is curved in the middle for strength, which means there is less chance of slicing your fingers if the blade slips and starts riding the metal.