The NYSE defines the symbol into two parts: a root and a suffix. The root constitutes the first part of the symbol and it can be up to six characters (although traditionally, most symbols representing companies only use a three-character root).

That said... in the early 00's, our is_nyse(ticker) function looked like: { return ticker.size() == 3; }

[1] https://www.nyse.com/publicdocs/nyse/data/NYSE_Symbology_Spe...

> Bankrupt electronics retailer Tweeter Home Entertainment soared nearly 1,000% in 2013 after Twitter (TWTR) filed to go public. That's because Tweeter's ticker was "TWTRQ" and Twitter had registered for "TWTR."