How do I create an indicator on the top to signal when the cell on the bottom is positive?

You could use a conditional format or a formula at the top of your sheet. With your number column in column A, select cell A1 and create a conditional formatting rule with a formula

=INDEX($A:$A,MATCH(99^99,$A:$A,1))<0

Select a format, for example a red fill. Any time the last number in column A is negative, cell A1 will turn red. If you want to mark positive numbers with green, create another rule with the formula

=INDEX($A:$A,MATCH(99^99,$A:$A,1))>=0

and use a green fill

Or use a formula in cell A1

=if(INDEX($A:$A,MATCH(99^99,$A:$A,1))<0,"negative","positive")

cheers, teylyn