A batsman had been given the benefit of the doubt when a catch close to the ground was made at gully at Blacktown International Sportspark.
When the umpire gave not out, Clarke used the T sign or player decision review signal intimating the decision should be reviewed by the third umpire.
However, Sheffield Shield matches are not televised and thus a third umpire is not used.
The code of behaviour states that if any player uses the T sign, even in humour, it will lead to an automatic report because it shows dissent at the umpire's decision.
Clarke was reported by the umpires for breaching Article 2.1.3, a charge he admitted and he accepted match referee Daryl Harper's proposed penalty of a reprimand without the need for a hearing.
It was the 32-year-old's first offence in the past 18 months and came after he had made an impressive return to action following a six-week injury lay-off.
Clarke had missed Australia's limited-overs tour to India as he battled his ongoing back problems and his innings of 88 was welcome with the first Ashes Test in Brisbane just three weeks away.
- Sports & Recreation