ok well from the looks of the eye symbol it looks more like a third eye than an eye of horus to me but I could just be interpreting it wrong. If it is the eye of horus I can say I honesty don't know much about it, I only know the appearance of it because I googled it. I found this site though so maybe you'll find it useful
websiteif it's the third eye then to dream of a third eye it tyicaly means that your own inner abilities are awakening or trying to awaken of course being on a tomb it could be something completely different I'm not sure.
An eye on a tomb sounds very egyptian to me, maybe you were right about the eye of horus.
now that symbol you described on a flag sounds very much like alchemy to me. To dream of alchemy tends to mean: To dream of alchemy, signifies that you are going through a period of turmoil, inner transformation, and self-renewal. Although these may be tough and difficult times, it will have a positive outcome.
Then there is a picture I randomly found of a green lion devouring the sun, coincidentally or ironically or whatever it happens to also be something alchemical. so here's the definition or reference I found about that:
The alchemical "green lion" devouring the sun relates to the experience of consciousness being overwhelmed by violent, frustrated desires (often masked by depression)
Hope this helped maybe just a little. I hoestly just googled all of that stuff because off the top of my head I didn't know anything about those things. The only thing that I did know about was that the symbol does resemble a transmutatin circle of some sort which is used in alchemy. But of course this is also just my personal opinion and opinions and ideas can often be wrong.