Schedule k1 estates and trusts how to account for a loss, rather than a gain

In your question, I'm not sure which boxes/lines you are referencing as A* and C, but if the K-1 form box has a negative amount in it, then the amount should be entered as a negative when you are recording the trust K-1 in TurboTax.

Some of the boxes on the K-1 are presumed to be and programed as additions to income (for example:  interest, dividends and gains), therefore, in order to show a loss for a box labeled as a gain, the amount entered on the K-1 should be negative. 

Other boxes are presumed to be deductions (like box 11), therefore the amounts on the K-1 are positive and entered as positive numbers, but the software program will know those are amounts to be deducted since that is the purpose of box 11 and any others that strictly for deductions.