The limit for a ticker symbol on NYSE is six characters... from Section 2.1 of the NYSE Symbology spec [1]:
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; }
> 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."
The maximum, as provided by general consensus are 4 letters. The fifth letter, when applicable, signifies company status. "Q" for bankruptcy, "A" or "B" for class names, "E" for delinquent, "J" and "K" for voting and non-voting respectively, and so on. See https://www.investopedia.com/ask/answers/06/nasdaqfifthlette... (doesn't just apply to NASDAQ)
