The quote is from Gary Van Sickle in this week's PGA Tour Confidential on Golf Magazine's website. To be fair, I think the full context of what he said (in a discussion about Erin Hills, the U.S. Amateur and the upcoming U.S. Open) should be presented:
"Erin Hills is certainly difficult enough, long enough and big enough for the U.S. Open. Plus, it's almost all natural and there's over 650 acres of room. Corporate suites is the name of the game in championship golf now. Nobody wants to admit it but scenery, especially water, plays a big part in which courses we rate highly: Augusta, Pebble. Signature holes almost always have water in play on them. There are plenty of great courses without significant water hazards--Oakmont, for starters. But I'm not sure Erin Hills can ever escape the shadow of Whistling Straits to the north and its luscious lake views, not to mention its PGAs and Ryder Cup."
To me, defining "signature hole" is akin to defining obscenity...subject to all sorts of qualifiers and audience/local standards. Some use the term interchangeably with "most photogenic hole." To some, it is the "most dramatic hole." In some cases, it is like splitting hairs. At Augusta, is it 12, 13 or 15 (or others)? At Pebble, is it 7, 8, 9, 10 or 18?
To me, it is a marketing ploy plain and simple. The signature hole is the one that ends up in magazine advertising.
In many ways, I think it is a pyrrhic designation because it seems to imply that the sum of one hole is greater or more appealing than the entire round at a particular course. Perhaps if the designation was "iconic hole," the field would be narrowed quite a bit.
As an aside, the whole "signature" business seems to have turned into a dumpster fire. In the Columbus area, there is a club that advertises itself as an "Arthur Hills Signature Design." That seems aimed at a very narrow...and probably very odd...niche of golfers.