May one read announcements placed on a bulletin board?
Those announcements which do not deal with matters of business, or mourning may be read.
May a list which one wrote before Shabbos be read on Shabbos?
[If they do not involve words of Torah] then they may not be read.
May one read words on a billboard or street sign?
 SSH”K 29/48
 SSH”K 29/49
 As since it is not recognizable to others that one is reading the signs, it should therefore be permitted, as is always the rule by Mimtzo Cheftzecha, that if it is not recognizable to others it is not forbidden. [306/1-2] So rules also Ketzos Hashulchan 107 footnote 9 that one may look for rent signs on houses on Shabbos. So is also clearly implied from 307/21 that reading in thought is permitted when not recognizable.
 Tzaruch Iyun from the ruling that one may not read the captions under paintings and the like [307/29], as in truth how can another person recognize whether he is reading the captions or looking at the picture. Vetzaruch Iyun.