The board of Noble, who own stamp specialists Apex and coins and medal specialists Baldwin's, as well as multi-discipline auctioneers Dreweatts and Bloomsbury, advised that there was no certainty that an offer would be made.
However, they also advised that they were likely to recommend acceptance unanimously if an offer were made of 255p per Noble share, comprised of 192.5p in cash and 62.5p in new Stanley Gibbons shares.
At least one source puts the value of the potential deal under these terms at £42m.
The boards of Stanley Gibbons and Noble both believe that the combination of the two businesses has considerable strategic and financial logic and will make further announcements as appropriate in due course.
The deadline for Stanley Gibbons to declare that they will or will not make an offer is 5pm on October 10.
"We are naturally restricted in terms of what we are able to say at this time," said Stephan Ludwig, executive chairman of Dreweatts & Bloomsbury Auctions and executive director of Noble.
"The prospective business synergies speak for themselves and we anticipate Stanley Gibbons raising the financing referred to in today's stock exchange announcement.
"In the meantime it is 'business as usual' for all of Apex, Baldwin's, Bloomsbury Auctions and Dreweatts as we head into a busy autumn season of extremely exciting sales."