I would laminate the sign and adhere magnets to the sign and magnet strip to your wagon - when you are not needing to 'advertize' you can just pull it off and put it away but the 'magnet strip' would remain looking like a 'racing strip' .... I am anal though and duct tape and other forms of adhering with 'tape' leaves a 'residue' that gunk sticks to between uses and over time your Choo choo wagon will get icky looking?
You can also get a magnetic sign from somewhere like Vista print with your logo on it - and adhere it that way and they are meant to be out in 'weather' so you could leave it on and not have to worry about fading by the sun and so forth - I got these for my van and love them!
. Funny you should mention the magnetic sign from Vista; I do have one (posted on my front door); could easily order another...magnetic racing stripe; fantastic! Agreed; did not want to have the wagon get icky. Thankyou Thankyou!
Children are great imitators.
So give them something great to imitate.