Teach your toddler the equal sign when he or she is starting simple arithmetic exercises. This is also an abstract concept when taken outside of a mathematical context, so you can show gradual examples of how people are 'equal' regardless of gender, race, age, and so forth. "Daddy is equal to Mommy. We just do things differently..."
This is a useful flash card taught best in conjunction with other simple mathematical operations. Outside of arithmetic, you can also teach the concept of 'equal' along with fairness at play, taking turns, sharing, and so on.