The phrase "a discreet form" is correct and usable in written English.
It can be used when referring to a manner or method that is careful and unobtrusive, often in the context of maintaining privacy or subtlety.
Example: "She chose a discreet form of communication to discuss sensitive matters without drawing attention."
Alternatives: "a subtle manner" or "a private method".
The White House press secretary, Jay Carney, declared that ZunZuneo was a "neither covert nor an intelligence program," preferring instead to call it a "discreet" form of humanitarian assistance to Cubans who lived in a "non-permissive environment".
Asked if Parsley's presence in prison in any way represents a discreet form of Upper East Side social commentary, Olle would only paraphrase Parsley's own observation, that the Upper East Side and prisons "are gated communities that suffer from an imbalance of power".
Remember that pointing with your eyes and a nod of your head is a most discreet form of pointing.
They said that the device is "almost invisible", providing a more discreet form of protection against dirty air than the large masks covering the lower half of the face that are often sported by cyclists in polluted city streets.
The injection is a discreet, reliable form of contraception and is now the most popular form of contraceptive in sub-Saharan Africa, accounting for 41% of all modern contraceptive use.
Since its discreet form factor doesn't feature a screen, the Motiv's battery can last three to five days on a single charge.
Church officials had suggested that prayers for Mr. Priebke, "which had not been denied," should be held in "reserved and discreet form" in the house where Mr. Priebke had lived and died, the residence of his lawyer, Paolo Giachini.
To cap it all (and to the great consternation of the Americans in the audience), a white ram is sacrificed, its bloody corpse later dumped out of sight behind a drinks booth, where it will no longer offend eyes accustomed to more discreet forms of butchery.
So were other, more discreet forms of adultery.
On the other, chilled by the Prevent strategy, they feel obliged to send out discreet forms to invited speakers that aim to pre-censor their talks or, at any rate, offer early warning of "trouble".
