If it depends on how much has happened in the subregion your fortress belongs to, then, I guess, when playing a small world with little worldgen history and/or no towns/caves/previous abandoned forts in your area - you're limited to things that happened in your current fort.
My 20-year-old fortress in a small world has almost all engravings like one of these:
dwarves laboring/travelling (i.e. foundation of the fortress);
expedition leader surrounded by dwarves;
random dwarf or dog striking down some goblin;
random dwarf is raising the <insert artifact or masterwork item name here>;
civ symbol (a backpack);
local group symbol (oddly, a giant; silly me, wondering why there are lots of giants engraved);
lots of large roaches/cave spiders/whatever vermin the engravers happen to hate;
lots of random nonhistorical things, like blazing suns or crescents, made when the engravers were less experienced.
I found one strange engraving though. It was something like "an image of Mistem McLeader and buckets. Mistem McLeader is surrounded by the buckets". I bet that's dwarven humour, 'cause on all other engravings he is surrounded by dwarves.
Oddly enough, there is not a single image of my liaison suddenly dropping dead in the middle of a meeting (she died of old age, as I've later found out in legends). Looks like that death from natural causes does not count as notable event.
I think I'm going to play some adventurers to enrich the world's history before attempting another long-term fort.