Everything falling into place for L?
He might have noticed Misa in the women's magazine. If memory serves me correctly, L mentioned that one of second Kira's victims was only present in a woman's magazine.
Strands of hair was found on the evidence. When he sees Misa for the first time and smiles, he's clearly looking at her hair. Then follows by saying she has a unique style. Possibly hinting that there aren't many blonde women Raito, the suspected Kira, comes into contact with. Raito's sudden change in behavior, dating multiple women, to throw off being seen with Misa. The second Kira.
The detective following Raito around no doubt reported seeing him with a blonde woman. L might have recalled the magazine. It falls perfectly into his theory that Kira and the second Kira had already met. Now he's letting Raito know that he knows. Misa really made things easy for him with her obsession over Raito. At the very least, prolong his life.
Excellent chapter, this manga is getting good!