Previously, a single company could have many different ticker symbols as they varied between the dozens of individual stock markets.
Today, Daimler AG stock trades on twenty-two different stock exchanges, and is priced in five different currencies; it has the same ISIN on each (DE0007100000), though not the same ticker symbol.
–For trade identification
In this case, ISIN cannot specify a particular trade, and another identifier (typically the three- or four-letter exchange code such as the Market Identifier Code) will have to be specified in addition to the ISIN.
–For price identification
The general public would want the price for an ISIN, while traders may want the price for a ticker symbol on one (or a few) liquidity venues.