Characteristics of survival coins
Stamped in universal language: Survival coins must be stamped in a universal language such as English or at least in a language that will be understandable in the country of its intended use. E.g. the majority of Americans only understand English.
Comfortable fractions: The silver coins intended for survival purposes should contain fractions that are comfortable to use in the country of its intended use. E.g. Americans are comfortable with 1-ounce, 1/2-ounce, 1/4-ounce, and 1/10-ounce coins.
Silver content stamped on coins: This is not a vital requirement, but it will definitely help if the silver content is stamped on silver coins intended to be used for survival purposes. It will much easier to convince someone to accept silver coins if the silver content is clearly stamped on the relevant coins than otherwise.