I guess you mean this thread. Under normal circumstances, it’s not necessary to do anything special to block these messages. Through normal training, SpamSieve will rapidly learn that your good messages don’t use these characters. Before doing anything else, you should use the log to see whether these messages are actually getting through SpamSieve.
Secondly, if you look at the headers of a spam message, the Content-Type will tell you which charset it uses. You can then create a blocklist rule that matches that character set.