Not at the very beginning. But when they first added ads, they were clearly marked in the top with a yellow background (and they didn't take over the whole page), and on the righthand column (and they were clearly marked as sponsored links).

I'd have to dredge it up but someone put up a site that showed the visual changes to ads over the past 15 years, and they've become more and more indistinguishable from organic search results, and they've taken over more of the page.

A great visual history of enshittification, and also how "growth at all costs" capitalism leads to that enshittification. Google was still taking in money hand over fist in the mid 00s when they had a few, clearly marked ads, but capitalism demands the line arcs upwards no matter what.