The correct answer is "in".
Market history: Jonathan's Coffee House
Public auctions have been held for hundreds of years, allowing merchants to buy commodities at a future point in time (futures or forwards). The markets have grown and become largely electronic, however in certain exchanges like Frankfurt and the NYSE, you can still trade on the floor (in the pit).
Financial markets today are still markets despite the fact that most of the trades are conducted remotely.
Definition of market
- A regular gathering of people for the purchase and sale of provisions, livestock, and other commodities.
- An area or arena in which commercial dealings are conducted.
Therefore you buy or sell in a financial market, in the same way you would buy or sell in a flea market.
The rise of "on the market"
The use of on the market has increased for a few reasons.
Firstly, because "bond market" has become so over complicated that it is seen to be a black box. You would act on a box.
Secondly, because "stock" markets show listings, the original stock markets were chalk boards matching buyers and sellers, so technically you could chalk up your sale on the board or on the stock exchange listing. However, unless you are referring explicitly to listing a trade on a chalkboard (which they still do in some emerging markets), then again, you are referring to activity in the market.
NOTE: This contradicts a similar answer in the "english language" forum which suggests that the bond market is an abstraction. However, after many years working in the investment banking sector, I can assure you that there is nothing abstract about the bond market. The market works on fundamentally the same principles as conception many centuries ago, but with larger volumes, faster transactions and on computers instead of chalkboards.
So this is not about the use of the prepositions on/in, this is about the definition of "bond market", which is not some esoteric object but which is (or should be) a simple exchange of products.