Replace the duplicated “greater than” (>>) or “less than” (<<) symbols by guillements (« and »).
From the UML specification:
Guillemets are a special kind of quotation marks and should not be
confused with or replaced by duplicated “greater than” (>>) or “less
than” (<<) symbols, except in situations where the available character
set may not include guillemets.
Replace the duplicated “greater than” (>>) or “less than” (<<) symbols by guillements (« and »).
From the UML specification: