well, as for icons, you can do a search for
updated icons and you'll see soemthing like this:
As you may see, they're not conceptually descriptive and they're quite ambiguous.
However, here you need to ask yourself: do you want users to know an action was performed, or do you want users to know the result of that action? For example: do you want your users to know a cell was updated/modified/deleted/whatever so they can act on consequence, or do you want the users to know how data inside that cell has been affected? This makes a difference, because if what you want is for users to know the action was performed, then you can use the exclamation mark icon , which is a sign of warning and attention needed (see it's one of the icon's proposals)
If we're talking about content affected by the action the user has performed, you'll also see that the most common icon for "updated" (the circular arrows) is commonly used for change as well as reload, so they're not semantically unambiguous, thus you should look for something more concrete. IMHO, your best bet is.... the word "updated"
Optionally, you could use a color system, and simply have a color reference for that system. For example, you could define
green as the color for updated items and grey for default items. Simply have a small reference before your board that tells the user what the color reference means