I googled 'free large dog vest pattern' and found this...

Here is a link that might be useful: dog vest pattern

The local VFW ladies made vests for themselves for parades and used window screening....not the metal stuff, but the vinyl. I bet you could make dog vests and attach letters to the screening. It would keep them cool too!
Kathy G in MI

thank you both for the info - the vinyl screening is a great idea. I'll check Home Depot next time I go out.

Hi, Barbara,

I had to re-design/enlarge a small-sized pattern to make a larger pattern in order to make a vest for a friend's 8 lb dog. If you want, I could draw out another pattern for you and send it by snail mail, and you could use it as a starting point and enlarge it as needed. Send me an email if you are interested and I'll get it out to you.

Sooz