I want to know the answer to the following question:
What has their been a prominent supply of in the 20th century?
All the background I'm provided with is that "Compare this with the use of symbols as names in 20th century musical albums such as Led Zeppelin IV (1971) and Love Symbol Album (1993); an album cover may potentially contain any graphics, but in writing and other computation these symbols are difficult to use.". Is that enough to answer the question?