Predicted number of signals in proton NMR spectroscopy
Since there isn't free rotation around the C=C bond in the alkene, the two hydrogens, Ha and Hb are experiencing different electronic environments. Whenever two hydrogen atoms are experiencing non-identical electronic environments, they are going to possess differing chemical shifts in proton NMR. If you heat this compound, and it doesn't decompose, I would expect the two signals from Ha and Hb to coalesce into one as the hindered rotation about the alkene C=C bond becomes unhindered. 

https://chem.libretexts.org/Textbook_Maps/Organic_Chemistry/Book%3A_Organic_Chemistry_with_a_Biological_Emphasis_(Soderberg)/Chapter_05%3A_Structure_Determination_II/5.2%3A_Chemical_equivalence