I would guess that sentence: "that sank 2600 years ago" would imply that we are not talking about exact date. But more explicit word like: "that sank about 2600 years ago" would help.
Using different number formatting instead of word or sign (~) is still implicit and not explicit.
Unless the precision (resolution) is known (stated), it is unclear whether the trailing zeroes are significant or not, one may only guess (while such a guess looks reasonable in this case). A convention for writing that unambiguously is to avoid insignificant trailing zeroes: e.g., writing it as 26e2 or 2.6e3. Then the written number carries along its precision.
This reminds me of Andrew Scott Waugh, who surveyed the height of Mount Everest. He was sure his method was accurate to the nearest foot but he measured the height of the mountain at exactly 29,000 feet.
Since he thought people would assume it was a rounded figure, he reported it as 29,002. And is therefore known as the man who first put 2 feet on the top of Everest.
In contexts significant figures might be relevant, a bar over the last 0 or a decimal point at the end are the easiest methods of saying "no really, these 0s are the real deal". Though you have other options like scientific notation, an explicit uncertainty bound, or natural language context too https://en.wikipedia.org/wiki/Significant_figures#Ways_to_de...