“Should someone be able to tell I’m interested, or do I need to make it clearer?”
tl;dr, no - they probably can't tell your interested, you should make it clearer.
As humans, we have a self-centered bias that makes us think that our intentions should be obvious to others. If I like someone, it should be so clear to them that I like them. Unfortunately, that isn't really how it works.
There are two big problems with this line of thinking: First, people are really bad at assessing the intentions of the people they are interested in dating [1]. Second, signals of romantic liking and platonic liking (people I want to date vs people I want to be friends with) are really similar.
Signals of romantic interest can be blurry when you are friends with someone. For women, certain kinds of behaviors are normal in a friendship, like sharing personal feelings and disclosing private information. For men, that behavior may be less common in their friendships with other men; therefore, when a friend who is a woman engages in that kind of behavior with them, it may signal intimacy that wasn't intended by that friend.
Some research has found that people are more likely to pick up on pulling away signals in a relationship than they are to pick up on escalating signals [2]. In other words, when a friend starts to pull away, people are more likely to infer that their friend is not interested in being their friend than to infer changes to that relationship when that friend starts becoming more friendly. As signals of intimacy increase, people are more likely to explain that away in their head to avoid dealing with changes in the relationship. "They aren't interested in something more with me, they just really like me as a friend."
Even if you are giving all of the signals that you are interested in something more, your friend is more likely to explain that away than to think you are interested in them romantically. The best way to ensure the other person knows you are interested is to very clearly let them know you are interested. It is a kindness to others to tell them when your expectations and desires for the relationship have shifted. If you wouldn't want to be their friend if they turn you down, pretending to be their friend is unkind.
References:
- Haselton, M. G., & Buss, D. M. (2000). Error management theory: a new perspective on biases in cross-sex mind reading. Journal of personality and social psychology, 78(1), 81.
- Floyd, K., & Voloudakis, M. (1999). Attributions for expectancy violating changes in affectionate behavior in platonic friendships. The Journal of Psychology, 133(1), 32-48.