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The signs matter for the sake of operations subtraction and addition.

Similar terms are terms with exactly the same literal coefficients, meaning same variable (represented by letter) and its exponent.

1)  -xy²,   4xy²,   -¹/₃xy²  are similar terms. They have the same literal coefficients xy².

2)  4x²y, 5xy²  are both positive terms but they don't have the same literal coefficients.  x²y  and xy²  are not the same. These terms are not similar.
Add:  The answer is "Yes", IF the literal coefficients are the same, whether negative, or positive.