The phrase "a serious mark" is correct and usable in written English.
It can be used to refer to a significant or notable indication of something, often in a context where the seriousness of the mark is emphasized.
Example: "The report showed a serious mark of decline in sales over the last quarter."
Alternatives: "a significant indicator" or "a notable sign".
Under current legislation parents can hit a child if it constitutes "reasonable chastisement" and does not leave a serious mark.
As for his team, the Galaxy remains talented enough to leave a serious mark on the under talented or unprepared.
Another year goes by where Arsenal won't make a serious mark in the Champions League; despite their qualification being justification for Wenger keeping his job year on year.
Here's the turbulent priest: "Becket was the first Londoner to make a serious mark... with an instinctive flair for... display and costume, the getting and spending of money, theatre and even though his stomach was delicate, fine food and drink.
"Better efficacy and higher bleeding, including fatal bleeding — it's a question mark, a serious question mark, both regulatory and commercial".
"From my point of view, the report placed a serious question mark over the proposal.
Lewis D. Lowenfels, a New York lawyer and expert on securities law, called the possible charges "a serious black mark" against the company.
Being identified as a gang-member can be a serious black mark, warranting a stiffer than average sentence for any crime.
"It's a serious question mark," said Representative Jason Chaffetz, a Utah Republican who is the chairman of the House oversight committee's national security subcommittee.
Dripping with top-five left-tackle-type talent early in his career, durability problems have made the 26-year-old a serious question mark.
"It puts a serious question mark over Russia's respect for international obligations of fair, transparent, and independent legal process," she said.
