Is it just to display a text popup or is it also clickable to run a macro etc?

Just to display a text popup for informational purposes. The alternative is to use Data Validation, just using the Input Message tab. The user clicks the cell and the message pops up. It works better than inserting a New Note. But I think even better would be a hover feature which might be more flexible about size and number of characters.

Is the icon/symbol an image/picture? I was thinking about using hyperlink as it contains captions. The hyperlink for the image could be disabled (with VBA) but the caption will still show when the mouse hovers over the image/picture. Is it acceptable? 

I experimented with this approach, attached. You can't hyperlink an image (that I know of) but you can hyperlink a cell with a ScreenTip. The hyperlink destination refers to the same cell so it doesn't go anywhere even if you click it. is this what you had in mind?

You can hyperlink an image. Refer my attachment.

You will need to run the attached macro for each image.

Just change the image's name and the tool tip.

Hope this helps.

This is interesting. If I add a lot of text it displays as one long line. What if want to have text wrap?

You can try adding a carriage return like this to the code.

"Message at row 1" & vbcr & "Message at row 2"  & vbcr & "Message at row 3" etc

No idea what is the maximum length allowed.

Good luck