The phrase "as a flag for" is correct and usable in written English.
It can be used to indicate a symbol or indicator for something, often in a metaphorical sense.
Example: "The sudden increase in sales served as a flag for the company's growing popularity in the market."
Alternatives: "as a signal for" or "as an indicator of".
If this does not kill the invader outright, then it acts as a flag for the bug in question to be eaten by a macrophage.
Even if only one punter bought it - unlikely, since the most popular of these prints sold in their hundreds - the image stands as a flag for what was still "thinkable and doable" during that dark, difficult year of 1819, when scores of working men and women protesting against the government's increasingly jittery attitude to democratic freedom were mown down at Peterloo.
More specifically, only one reserved "bit" is used as a flag for locality, where the value 0 indicates a local scope and the value 1 indicates a global one.
So now you can buy me, Mawky, as a flag for yah frunt yahd.
The short-lived Frankfurt Parliament of 1848 1850 proposed the tricolour as a flag for a united and democratic German state.
Humphrey Atherton, a prominent Massachusetts official and one of Dyer's persecutors, wrote, "Mary Dyer did hang as a flag for others to take example by".
Pardon the bad joke, but you might see it as the officials throwing a flag for too many CEOs on the field.
Athletes from both nations entered Pyeongchang Stadium as a unified team sharing a flag for Friday's opening ceremony.
Plus, as previous attempts to create a flag for the Earth were determined aesthetic failures, even if we don't make it to Mars, we at least now have a symbol to under that isn't geopolitically charged.
A Catholic notion of redemption retained some potency for him, and he was not above an occasional naturalistic deployment of conventional religious imagery (as in the glorious finish of "A Flag for Sunrise").
Fracked gas featured as a flag carrier for extending the life of the second industrial revolution.
