Here is an example of how to display a matrix with both negative and positive values in Python: 

matrix = [[1, 2, -3], [-4, 5, 6], [7, -8, 9]]

for row in matrix:
    for val in row:
        print(f'{val:4}', end='')
    print()

Output: 

 1   2  -3
  -4   5   6
   7  -8   9

In this example, we create a matrix with three rows and three columns, and some of the values are negative. Then we use a nested for loop to iterate through each row and each value in the matrix, and print each value with a width of 4 characters, using a formatted string (f'{val:4}'). We end each row with print() to move to the next line.