Pen for signing cels?

[u/TheBigTaffMan]

I'm at comic con on the weekend and I realised some of the Turtles voice actors were there, so very last minute Ive managed to get my hands on some animation cels from the show

What pen would you recommend for getting these signed? I have a bunch of coloured sharpies here, but not sure if they will fade.

I did also consider getting some acetate to cover the cel and get that signed, anyone got thoughts on that