Here I am, asked by my local Chinese takeaway to sort out their sign across the width of the shop with "DELIVERIES AVAILABLE" and their phone number. I start by cleaning up the rust (with a combination of angle grinder and rust converter). I then metal prime, undercoat and paint it an ultramarine blue (exterior gloss for its weathering properties), and sign write the text in an appropriate font, colour and paint (in this case Franklin Gothic Medium, in white and with "One Shot" Sign Painters' Lettering White).
Here's a Top Tip for people who aren't regular professional signwriters (like me!)
Print off your lettering to the finished size on A4 paper.... use a compass or other such instrument to pin prick through the outline of the letters...stick the lettering together with masking tape making sure it is perfectly straight, level and well spaced out...then on site, sponge chalk through the holes in the paper to leave a pointillist image of the letters to paint over as a guide. With a fairly confident hand, you should be able to achieve excellent results!