@jw A considerate idea, but unless you have to distinguish the arrow from, say, an elephant, then no. It could even be detrimental. Many people find alt text useful, including those on slow Internet connections, but especially blind people who may be listening to the page. Unnecessary words add to the page's size (a million visitors all get that extra stuff so it adds up), add to the time taken to listen to or load a page and would get annoying very fast.