The Grin coin was also added as an Android app to the Satoshi Bitcoin Converter app in the Google Play store at Satoshi Bitcoin Converter android app. It is suggested that you use the simple Satoshi Bitcoin Converter app, since it (a) does the same as this standalone Grin app, and (b) has multiple other crypto and fiat currencies. If you wish to stick with this app, no problem!
I've long pushed for the shi symbol シ to represent one satoshi in Bitcoin, get it? satoSHI. Reddit post here. On January 17, 2019, when Grin was just a two day old baby, the Grin coin developers held a governance meeting and adopted the ツ symbol (tsu) as the official symbol of Grin: Read meeting notes, section 10.2. To my eyes, the ツ symbol (tsu) is only slightly different than the シ symbol (shi). The fact that Grin adopted this symbol is great! Read the Gitter discussion here.
In early 2019, Ignotus Peverell, the founder of Grin, labelled the smallest unit of Grin as a "nanogrin" at gitter.im/grin_community/Lobby (screengrab below). In the Grin Converter app (and Satoshi Bitcoin Converter app), it's marked as an "Igno" as a tip-o'-the-cap to Ignotus. Like a "satoshi" being the smallest unit of Bitcoin, don't you think an "igno" is appropriate for the smallest unit of Grin?