Reddit mentions of Sign Painters

Yeah, it's kind of a lost art but there is a documentary about it and an accompanying book.

In short, not really. Graffiti tags / handstyles, no matter how weird and wild they are, still have typography roots. Many quality graffiti handstyles could be compared to quality sign painting styles – a lot of overlap. If you're looking to develop a clean, refined, and traditional style then studying traditional sign painting would be my recommendation. Calligraphy, typography (the study of type in general), and drawing letters in a traditional format will all contribute to your knowledge of lettering in general. Then graffiti styles will follow after studying and practicing it more. After I started getting really into type, hand lettering, and fonts in general is when I noticed my overall tag styles improve the greatest. The rest is just a ridiculous amount of practice. Like going through multiple phone books, thousands of pens, and cans of paint.

Here's some links, I haven't checked all the books personally but I have a few of them:

seanwes.com/learn/

http://www.amazon.com/Sign-Painters-Faythe-Levine/dp/1616890835/ref=pd_sim_b_2?ie=UTF8&refRID=18KCM0XRJB2Y65NMC6F7

http://www.amazon.com/Shadow-Type-Classic-Three-Dimensional-Lettering/dp/0500516995/ref=pd_sim_b_14?ie=UTF8&refRID=18KCM0XRJB2Y65NMC6F7

http://www.amazon.com/Mack-Brush-Freehand-Lettering-EDUCATIONAL/dp/B0046DK1EC/ref=pd_sim_b_9?ie=UTF8&refRID=18KCM0XRJB2Y65NMC6F7

http://www.amazon.com/The-Hand-Lettering-Helm-Wotzkow/dp/0486217973/ref=pd_sim_b_3?ie=UTF8&refRID=18KCM0XRJB2Y65NMC6F7

https://www.google.com/search?q=sign+painting+techniques&safe=off&espv=2&biw=1535&bih=1039&tbm=isch&tbo=u&source=univ&sa=X&ei=82p_VInZEsP7ggSK5oDQAg&ved=0CCYQsAQ

https://www.google.com/search?q=sign+painting+techniques&safe=off&espv=2&biw=1535&bih=1039&tbm=isch&tbo=u&source=univ&sa=X&ei=82p_VInZEsP7ggSK5oDQAg&ved=0CCYQsAQ#safe=off&tbm=isch&q=hand+drawn+letter+techniques

One of my favorites:
https://www.google.com/search?q=herb+lubalin&safe=off&hl=en&biw=1535&bih=1039&source=lnms&tbm=isch&sa=X&ei=5Gt_VKa8BcSVNqm1gbgJ&sqi=2&ved=0CAYQ_AUoAQ

for inspiration theres this: http://www.amazon.com/Sign-Painters-Faythe-Levine/dp/1616890835
also if you get the one with the appendix in the back it has a good few sheets of learning terminology, styles, how to etc

Sign Painters There's also a documentary as well.

Late to the game, but I saw this last summer and it's fantastic! A great story of a fascinating art form; totally well done. If anyone has the opportunity to see it, you should. There's an accompanying book as well that I own- http://www.amazon.com/Sign-Painters-Faythe-Levine/dp/1616890835/ref=sr_1_1?ie=UTF8&qid=1410302272&sr=8-1